Study of Human Body

Study of Human Body

(A) Digestive System

The complete process of nutrition is divided into five stages:

1. Ingestion

2. Digestion

3. Absorption

4. Assimilation

5. Defecation

1. Ingestion

• Taking the food into mouth is called ingestion.

2. Digestion

• Conversion of non-absorbable food into absorbable form. 

• The digestion of the food is started from the mouth.

Mouth (Buccal Cavity)

• Saliva is secreted by salivary gland in mouth in which enzyme amylase or ptyalin is present.

• Amylase converts starch into simple sugar and makes it digestible.

• In human, secretion of saliva is approximately 1.5 litre per day.

• The nature of saliva is slightly acidic (pH 6.8 to 7.3).

• From the mouth, food reaches into stomach through food pipe or oesophagus.

• No digestion takes place in food pipe.

• The teeth used for grinding of food is molar.

• The regular contraction and expansion of the wall of alimentary canal to push the food in forward direction is called peristaltic movement.

• In stomach, food is converted into chyme by the churning movement of its muscular wall.

• Spicy and pungent are not the tastes of tongue.

Digestion in Stomach

• The food lies approximately for four hours in stomach.

• After reaching the food in stomach, gastric glands secrete the gastric juice.

• This is a light yellow acidic liquid.

• pH of gastric juice is about 1.8.

• Hydrochloric acid secreted from the Oxyntic cells of the stomach kills all the bacteria coming with food and accelerates the reaction of enzymes.

• Hydrochloric acid makes the food acidic by which action of amylase on food stops.

• The enzymes in the gastric juice of stomach are Pepsin and Renin.

• Pepsin breaks down the protein into peptones.

• Renin breaks down the Caseinogen into Casein found in milk.

• Protein-digesting enzyme secreted by stomach is pepsin.

• In stomach, food is converted into chyme by the churning movement of its muscular wall.

Digestion in Intestine

Intestine is divided into two main parts:

(a) Small intestine

(b) Large intestine

Small Intestine

• It is subdivided into three parts — Duodenum, Jejunum, and Ileum.

Note: First enzyme which mixes with food in digestive tract of human is amylase in the buccal cavity or mouth.

Duodenum

• As soon as the food reaches the duodenum, bile juice from liver combines with it.

• Bile juice turns the acidic medium of food into alkaline.

• Here, pancreatic juice from pancreas combines with food. It contains three types of enzymes:

(a) Trypsin: It converts the protein and peptone into polypeptides and amino acids.

(b) Amylase: It converts the starch into soluble sugar.

(c) Lipase: It converts the emulsified fats into glycerol and fatty acids.

• Cholecystokinin is a hormone secreted by endocrine cells of duodenum which induces the release of digestive enzyme from pancreas and bile from gall bladder. It is also known as appetite suppressor.

Jejunum

• Here, the process of digestion is completed and absorption of digested food starts.

• From the wall of small intestine, intestinal juices secrete. The following enzymes are contained:

(a) Erepsin: It converts the remaining protein and peptone into amino acids.

(b) Maltase: It converts the maltose into glucose.

(c) Sucrase: It converts the sucrose into glucose and fructose.

(d) Lactase: It converts the lactose into glucose and galactose.

(e) Lipase: It converts the emulsified fats into glycerol and fatty acids.

• Intestinal juice is alkaline in nature.

• In a healthy person approximately 2 litres of intestinal juice secretes every day.

Ileum

3. Absorption:

• Digested food gets mixed into blood — this is called absorption.

• The absorption of digested food takes place through villi found in the wall of small intestine or ileum.

4. Assimilation

• Use of absorbed food in the body is called assimilation.

Large Intestine

5. Defecation

• Undigested food reaches into large intestine where bacteria turns it into faeces, which is excreted through anus.

Note:

• Enzymes are biocatalysts.

• Root of tooth is covered by cementum.

• The pouch connected to the junction of small and large intestine is called caecum.

• Digestion of food is completed in small intestine.

• Complete digestion of fat takes place in small intestine.

• Small intestine is longer than the large intestine.

Summary of Digestion

S. No	Gland Juice	Enzyme	Edible Substance	After Reaction
1	Saliva	Amylase	Starch	Maltose
2	Gastric Juice (1)	Pepsin	Protein	Peptones
	(1) Rennin	Casein	Calcium paracasein
3	Pancreatic Juice (1)	Trypsin	Protein	Polypeptides
	(11) Amylase	Starch	Sugar
	() Lipase	Fat	Fatty acid and glycerol
4	Intestinal Juice (1)	Erepsin	Protein	Amino acid
	(1) Maltase	Maltose	Glucose
	(Lactase)	Lactose	Glucose and fructose
	(iv) Sucrase	Sucrose	Glucose and galactose
	(V) Lipase	Fat	Fatty acid and glycerol

The Main Organs Participating in Digestion

Liver

• This is the largest gland of the human body. Its weight is approximately 1500 gram.

• Bile is secreted from liver. This bile accelerates the action of enzymes present in the intestine.

• Liver converts excess of amino acid into ammonia by deamination. These ammonia are further converted into urea by ornithine cycle. Urea comes out from body through kidney.

• Liver can convert some quantity of protein into glucose during deficiency of carbohydrate.

• In carbohydrate metabolism liver converts the excess of glucose found in blood into glycogen and stores it into hepatic cell as reserve nutrients.

• If the necessity of glucose arises, the liver converts glycogen into glucose. Thus, it regulates the quantity of glucose in the blood.

• In case of decrease of fat in food, liver converts some parts of carbohydrates into fat.

• The production of fibrinogen protein takes place by liver which helps in clotting of blood.

• The production of Heparin protein takes place in liver which prohibits the clotting of blood inside the body.

• The dead RBC is destroyed by the liver only.

• The liver reserves some quantity of iron, copper, and vitamins.

• It helps in regulating the body temperature.

• Liver is an important clue in investigating a person's death that has been due to poison in food.

Gall Bladder

• Gall bladder is a pear-shaped sac, in which the bile coming out of liver is stored.

• Bile comes into the duodenum from gall bladder through the bile duct.

• Secretion of bile into the duodenum takes place by reflex action.

• Bile is a yellowish-green coloured alkaline liquid. Its pH value is 7.7.

• The quantity of water is 85% and the quantity of bile pigment is 12%.

• The Main functions of bile are as under:

1. Bile makes the pH of the food alkaline and facilitates action of pancreatic juice.

2. It kills the harmful bacteria coming with food and neutralizes the acidic pH of food coming from stomach.

3. It emulsifies the fats.

4. It accelerates the bowel movement of intestine by which digestive juices in the food mix well.

5. It is helpful in the absorption of vitamin K and other vitamins mixed in fats.

• In case of obstruction in bile duct, liver cells stop taking bilirubin from blood. As a result, bilirubin spreads throughout the body. This is called jaundice.

Pancreas

• This is the second largest gland of the human body. It acts as simultaneously endocrine and exocrine type of gland.

• Pancreatic juice secretes out of it in which 9.8% water and the remaining parts contain salt and enzymes.

• It is alkaline liquid, whose pH value is 7.5–8.3.

• It contains the enzymes which can digest all the three types of food materials (like carbohydrates, fat and protein), therefore it is called complete digestive juice.

Islets of Langerhans

• This is a part of the Pancreas.

• It was discovered by the medical scientist Langerhans.

• From its ß cell – insulin, from α cell – glucagon, and from δ cell – somatostatin hormones are secreted.

Insulin:

• It is secreted by β-cell of islets of Langerhans.

• Glucagon is secreted by α-cell and somatostatin hormone is secreted by δ-cell of islets of Langerhans.

• Insulin was discovered by Banting and Best in the year 1921.

Biology:

• Controls the process of making glycogen from glucose.

• Diabetes is caused due to the deficiency of insulin.

• Excessive flow of insulin causes Hypoglycemia, in which one loses consciousness and visual disturbances.

• Glucagon reconverts the glycogen into glucose.

• Somatostatin: This is a polypeptide hormone which is known as inhibitory hormone. It inhibits the secretion of other hormones as well as activity of pancreatic hormone like insulin & glucagon.

• Malfunctioning of pancreas causes diabetes.

• Insulin is essential for uptake of glucose by cells of body.

(B) Circulatory System

• The discovery of blood circulation was done by William Harvey in the year 1628.

• There are four parts under it:

(a) Heart

(b) Arteries

(c) Veins

(d) Blood

Heart

• It remains safe in the pericardial membrane. Its weight is approximately 300 grams.

• Heart of the human is made up of four chambers.

• At the anterior side there is a right atrium and a left atrium.

• In the posterior side of the heart there is a right ventricle and a left ventricle.

• Between the right atrium and the right ventricle there is a tricuspid valve.

• Between the left atrium and left ventricle there is a bicuspid valve.

• The blood vessels carrying the blood from the body towards the heart is called vein.

• In vein there is impure blood i.e. carbon dioxide mixed blood. Its exception is pulmonary vein, which always carries pure blood.

• Pulmonary vein carries the blood from lungs to left atrium. It carries pure blood i.e., oxygenated blood.

• The main blood vessel carrying the blood from the heart towards the body is called aorta. This is the largest artery found in human.

• Arteries carry blood from the heart to different parts of body.

• In artery there is pure blood i.e. oxygenated blood. Its only exception is pulmonary artery.

• Pulmonary artery carries the blood from right ventricle to lungs. It carries impure blood.

• Right pulmonary artery is longer than the left.

• In the right part of the heart, there remains impure blood i.e. carbon dioxide mixed blood, and in the left part of the heart there remains pure blood i.e. oxygen mixed blood.

• The artery carrying blood to the muscles of the heart is called coronary arteries. Any type of hindrance in it causes heart attack.

Course of Circulation

• Mammals have double circulation. It means blood has to cross two times from heart before circulating throughout the body.

• Right atrium receives impure blood from the body which goes into right ventricle.

• From here the blood goes into pulmonary artery which carries it to the lungs for purification.

• After purification it is collected by pulmonary vein which brings it back to heart in left atrium.

• From atrium it goes into left ventricle. Now this purified blood is sent into aorta for different organs of body.

• This circulation is done in a cardiac cycle.

Cardiac Cycle

• Rhythmic systole (Contraction) and diastole (Relaxation) of auricle and ventricle constitutes a cardiac cycle.

Heart Beat

• Heart keeps beating rhythmically throughout life.

• There is a node from which contraction of heart originates known as SA node.

1. Sinoatrial node (SA node):

   • It is a specialised area of cardiac muscle fibre in right auricle.

   • SA node is also known as pacemaker as it generates each wave of cardiac impulse.

2. Atrioventricular node (AV node):

   • AV node is present close to the interatrial septum near the right AV aperture.

   • Wave of contraction is picked up by AV node which spreads through AV bundle of muscle fibres present in interatrial septum as well as inter-ventricular septum.

Artificial Pacemaker:

• When SA node becomes defective or damaged, the cardiac impulses do not generate.

• This can be cured by surgical grafting of an artificial pacemaker (an electric device) in the chest of the patient.

• It stimulates the heart electrically at regular intervals.

• Systole and diastole of the heart are collectively called heart beat.

• In normal condition, the heart of human beats 72 times/minute and in a single beat it pumps approximately 50 to 80 ml blood.

• The blood pressure of a normal human is 120/80 (Systolic 120 and Diastolic 80). These numbers represent the blood pressure at ventricular contraction and ventricular relaxation.

• Blood pressure is measured by sphygmomanometer.

• Thyroxin and adrenaline are the hormones which independently control the heart beat.

• The CO₂ present in the blood accelerates the heart beat by reducing the pH.

• Presence of air bubble in blood stream is dangerous to life because it may obstruct the flow of blood.

• Arteries and veins are connected together by capillaries.

(C) Lymph Circulatory System

• The light yellow fluid found in the inter-cellular space between different tissues and cells is called lymph.

• Lymph is a fluid whose composition is like blood plasma, in which nutrient, oxygen and various other substances are present with WBC.

• The corpuscles found in lymph are lymphocytes. In fact, these are White Blood Corpuscles (WBC).

• Lymph flows only in one direction — from tissue towards heart in lymph vessels.

Functions of Lymph:

1. The lymphocytes present in lymph help to prevent the body from diseases by killing the harmful bacteria or other toxic foreign bodies.

2. The nodes found in lymph vessels are called lymph nodes which work as a filter of microbes in the human body.

3. Lymph helps in healing the wounds.

4. Lymph helps in circulating different material from tissues to veins.

(D) Excretory System

Excretion

• Removal of waste product formed during metabolism, from the body of human is called excretion.

• Normally excretion means the release of nitrogenous excretory substances like urea, ammonia, uric acid etc.

The Excretory Organs of Human Are:

1. Kidneys

2. Skin

3. Liver

4. Lungs

1. Kidneys

• The main excretory organ in human and other mammals is a pair of kidneys. Its weight is 140 grams.

• There are two parts of it: Outer part is called cortex and the inner part is called medulla.

• Each kidney is made up of approximately 1,30,00,000 kidney ducts which are called nephrons.

• Nephron is the structural and functional unit of the kidney.

• There is a cup-like structure in every nephron called Bowman’s capsule.

• Glomerulus is made up of thin blood vessels found in the Bowman’s capsule which is made up of two types of arterioles:

(a) Afferent arteriole: Which carries the blood to the glomerulus.

(b) Efferent arteriole: By which the blood is taken out of the glomerulus.

• The process of filtration of liquid into the cavity of Bowman’s capsule is called ultrafiltration.

• The main function of the kidneys is purification of blood plasma i.e., to excrete the unwanted nitrogenous waste substances through urination.

• The supply of blood to the kidneys takes place in large quantity in comparison to other organs.

• In the kidneys, average 125 ml per minute blood is filtrated i.e. 180 litres per day.

• Out of it, 1.45 litres urine is formed daily and the remaining is absorbed back by the cells of nephron and mixed into the blood.

• Urine is an aqueous solution in which 95% is water. Other constituents are urea, uric acid, chloride, sodium, potassium, creatinine, organic and inorganic compounds.

• The colour of the urine is light yellow due to the presence of urochromes in it. Urochrome is formed by the dissociation of haemoglobin.

• The correct sequence of organs that occur in the path of urine flow in human is 

  • Kidney ->  Ureter -> urinary bladder -> Urethra

• Urine is acidic. Its pH value is 6.

• The stone formed in the kidneys is made up of calcuim oxalate.

2. Skin:

• Oil gland and sweat glands found in the skin respectively secretes sebum and sweat.

3. Liver:

• Liver cells play the main role in excretion by converting more and more amino acids and ammonia of blood into urea.

4. Lungs:

• The lungs excretes two types of gaseous substances carbon dioxide and water vapour.

• The excretion of some substances like garlic, onion and some spices in which vapour component is present excreted by the lungs.

Nervous System

Under this system thin thread like nerves are spread throughout the body. After receiving the information of environmental changes from the sensitive organs, it spreads them speedly like electrical impulses and establishes working and coordinating among different organs.

Nervous System of human is divided into three parts:

1. Central Nervous System

2. Peripheral Nervous System

3. Autonomic Nervous System

1. Central Nervous System

• Part of the nervous system which keeps control on the whole body and on nervous system itself is called Central Nervous System.

• The Central Nervous System of human is made up of two parts: Brain and Spinal Cord.

• Brain is covered by membrane called meninges. It is situated in a bony box called cranium which protect it from external injury. Input and output nerves meet at central nervous system.

A. Brain

Structure of Brain

• Fore brain

• Mid brain

• Hind brain

• Corpora quadrigemina

• Cerebrum

• Thalamus

• Hypothalamus

• Cerebellum

• Pons

• Medulla

(A) Fore Brain

The weight of the brain of the human is 1336 grams.

(i) The function of the Cerebrum:

• This is the most developed part of the brain.

• This is the centre of wisdom, memory, will power, movements, knowledge and thinking.

• The analysis and coordination of muscular movement received from sense organs.

• It is the largest part of brain.

(ii) The function of Thalamus:

• It is the centre of feeling pain, cold and heat.

(iii) The function of Hypothalamus:

• It control the hormonal secretion of endocrine glands.

• Hormones secreted from posterior pituitary gland secrete through it.

• This is the centre of hunger, thirst, temperature control, love, hate etc.

• Blood pressure, metabolism of water, sweat, anger, joy etc are controlled by it.

(B) Mid Brain

The function of Corpora quadrigemina:

• This is the centre of control on vision and hearing power.

(C) Hind Brain

(i) Function of Cerebellum

• It is somewhat at the back of head and consist of two cerebellar hemispheres.

• It is the (Voluntary) centre for coordination of muscular body movements and maintenance of posture keeping body in balance.

• It is second largest part of brain.

(ii) Pons

• It acts as bridge carrying ascending and descending tracts between brain and spinal cord.

(iii) Medulla

• It is posterior most part of brain and continuous into the spinal cord.

• It connect and communicate the brain with spinal cord.

• It contain the cardiac, respiratory and vasomotor centre that control complex activity like heart action, respiration, coughing, sneezing etc.

• The brain of the human is situated in the cranium which protects it from external injury.

• Brain is covered by membrane called meninges.

Note: EEG (Electroencephalography) is done to know the function of brain.

Spinal Cord

The posterior region of the medulla oblongata forms the spinal cord.

Functions:

1. Coordination and control of reflex actions i.e., it works as the centre of the reflex actions.

2. It carries the impulses coming out of brain.

Note: Reflex action was first discovered by the scientist Marshall Hall.

This is an involuntary action taken by spinal cord. Reflex action takes place in a sequence through neural pathways in nervous system called reflex arcs.

The correct sequence of reflex arc:

• Receptor → Sensory Neuron → Relay Neuron in spinal cord → Motor Neuron → Effector Organ.

2. Peripheral Nervous System

• Peripheral Nervous System is made up of the nerves arising from brain and spinal cord. These are called cranial and spinal nerves respectively.

• There are sensory, motor and mixed nerves.

• There are 12 pairs of cranial nerves and 31 pairs of spinal nerves found in a human.

• The unit of nervous tissues is called Neuron or nerve cell.

3. Autonomic Nervous System

Autonomic Nervous System is made up of some brain nerves and some spinal cord nerves. It supplies nerves to all the internal organs and blood vessel of the body.

Langley first presented the concept of Autonomic Nervous System in the year 1921.

There are two parts of Autonomic Nervous System:

(a) Sympathetic Nervous System

(b) Parasympathetic Nervous System

Functions of Sympathetic Nervous System

1. It narrows the blood vessels in the skin.

2. By its action hair gets erected.

3. It reduces the secretion of salivary glands.

4. It increases the heart beat.

5. It increases the secretion of sweat glands.

6. It stretches the pupil of eye ball.

7. It relaxes the muscles of urinary bladder.

8. It reduces the speed of contraction & relaxation of intestine.

9. The rate of respiration increases.

10. It increases the blood pressure.

11. It increases the sugar level in the blood.

12. It increases the number of Red Blood Corpuscles in the blood.

13. It helps in clotting of blood.

14. Collective impact of this affects fear, pain and anger.

Functions of Parasympathetic Nervous System

The functions of this system is normally the opposite of Sympathetic Nervous System.

For example:

1. It widens the lumen of blood vessels except the coronary blood vessels.

2. It increases the secretion of saliva and other digestive juices.

3. The contraction of pupil is caused by this.

4. It creates contraction in the other muscles of the urinary bladder.

5. It creates contraction and motion in intestinal walls.

6. The effect of this nervous system collectively creates the occasion of rest and joy.

Skeletal System

The skeletal system of human is made up of two parts:

(a) Axial skeleton

(b) Appendicular skeleton

(a) Axial Skeleton

The skeleton, which makes the main axis of the body is called axial skeleton. Skull, vertebral column and bones of chest come under it.

• There are 80 bones in axial skeleton.

(i) Skull

• There are 22 bones in it. Out of these, 8 bones jointly protect the brain of the human known as cranium. The structure made up of these bones is called forehead.

• All the bones of the forehead remain joined strongly by the sutures.

• There are 14 bones in addition to this which form the face. Ear ossicles have six bones and hyoid is made up of one bone.

(ii) Vertebral Column

• The vertebral column of the human is made up of 33 vertebrae.

• All the vertebra are joined together by intervertebral disc.

• Vertebra is made flexible by intervertebral disc.

• We divide the whole vertebral column into the following parts:

• The first vertebra is called atlas which holds the skull.

1. Cervical region – 7 vertebrae

2. Thoracic region – 12 vertebrae

3. Lumbar region – 5 vertebrae

4. Sacral region – 5 vertebrae (fused together)

5. Caudal region – 4 vertebrae (fused together)

Functions of vertebral column:

1. Holds the head.

2. It provides the base to the neck and body.

3. It helps the human in standing, walking etc.

4. It provides flexibility to the neck and body by which a human can move neck and body in any direction.

5. It provides protection to spinal cord.

(b) Appendicular Skeleton

The following are the parts of it:

• Foot bones – Both hands and feet have 60 bones. Each limb consists of 30 bones.

• To hold the forelimb and hind limb on the axial skeleton in human there are two girdles. The girdle of forelimb is called pectoral girdle and girdle of hind limb is called pelvic girdle.

• Pectoral girdle joined with forelimb is called humerus and the bone from pelvic girdle joined to hind limb is called femur.

Functions of the Skeletal System

1. To provide a definite shape to the body.

2. To provide protection to soft parts of the body.

3. To provide a base to the muscles for joining.

4. To help in respiration and nutrition.

5. To form Blood Corpuscles.

Important Facts

• The total number of bones in a human's body – 206 to 208

• The total number of bones during childhood – 270

• The total number of bones of head (forehead-8, facial-14, ear-6, hyoid-1) – 29

• The total number of bones in vertebral column initially – 33

  • After development – 26 (5 sacral fuse into 1 and 4 caudal fuse into 1)

• The total number of bones of ribs – 24

• The longest and strongest bone of the body – Femur (bone of thigh)

• The smallest bone of the body – Stapes (bone of ear)

• Foramen Magnum is an aperture found in the skull.

The Name and Number of Bones of Some Specific Regions

Ear bones: Malleus (2), Incus (2), Stapes (2)

Bone of hand:

• Upper arm – Humerus (1)

• Fore arm – Radius & Ulna (2)

• Wrist bone – Carpals (8)

• Palm bone – Metacarpals (5)

• Finger – Phalanges (14)
  Total: 30

Bone of Foot:

• Thigh bone – Femur (1)

• Hind limb – Tibia fibula (2)

• Ankle bone – Tarsal (7)

• Sole – Metatarsal (5)

• Digits – Phalanges (14)

• Knee – Patella (1)
  Total: 30

Cartilage is the part of skeleton which is not hard as bone and can be bent (e.g., tip of nose). External ear of man is mainly made up of cartilage.

Note:

1. The muscles and bones are joined together by tendon.

2. The muscle which joins bone to bone is called ligament.

3. Tendon and ligament are examples of dense regular tissue.

4. Ligaments of human body are made up of yellow fibre.

Endocrine System

(a) Exocrine Glands

• Gland which have duct are called exocrine gland. Secretion of enzymes pass through it.

Examples: Digestive gland, Sweat gland, Mucous gland, Salivary gland etc.

(b) Endocrine Glands

• These are ductless glands. Hormones are secreted by these glands.

• Hormones are sent to the different parts of the body through blood plasma.

Examples: Pituitary gland, Thyroid gland, Parathyroid gland etc.

Functions and Effect of the Main Endocrine Systems of the Human Body and Hormone Secreted by Them

1. Pituitary Gland

• It is situated at the base of brain in a depression of sphenoid bone of the forehead. This is called sella-turcica.

• Pituitary gland is attached to hypothalamus by a stalk. Its weight is approximately 0.6 grams.

• Pituitary gland is also known as master gland. Its secretion is controlled by hypothalamus.

• The functions of the hormones secreted by Pituitary gland:

The functions of the hormones secreted by Pituitaty gland:

1. STH Hormone (Somatotropic hormone): It controls the growth of the body especially the growth of bones. By the excessiveness of STH cause gigantism and acromegaly in which height of the human grows abnormally. Lack of STH causes dwarfism in human.

2. TSH Hormone (Thyroid Stimulating Hormone): It stimulates the thyroid gland to secrete hormone.

3. ACTH Hormone (Adrenocorticotropic Hormone): It controls the secretion of adrenal cortex.

4. GH Hormone (Growth Hormone): It controls the functions of gonads.

   • (a) FSH Hormone (Follicle-Stimulating Hormone): In male it stimulates spermatogenesis in the seminiferous tubules of the testis. In female, it stimulates the Graafian follicles of the ovary to secrete the hormone Oestrogen.

   • (b) LH Hormone (Luteinizing Hormone): Interstitial cell stimulating hormone, secretion of testosterone hormone takes place in male and in case of female estrogen hormone secreted.

5. LTH Hormone (Lactogenic Hormone): Its main function is to stimulate secretion of milk in breasts for infants.

6. ADH Hormone (Antidiuretic Hormone): It causes increase in blood pressure. It is helpful in maintaining the water balance in the body and reduce the volume of urine.

Note:

• Hypothalamus is the part of brain which control emotional reaction in our body.

• Hypothalamus is located at the base of brain near pituitary gland, releasing hormone which regulate the synthesis and secretion of pituitary hormones.

• Hormone secreted from hypothalamus regulate the body temperature.

• The hormone serotonin is known to be helpful in coping with stress. It is secreted by neuron located in midline of brainstem.

2. Thyroid Gland

• This is situated below the larynx on both sides of respiratory trachea in throat of human.

• The hormones secreted by it are Thyroxine and Triiodothyronine.

• The hormone thyroxine contains iodine. Iodine is essential for production of thyroxin.

Functions of Thyroxin

1. It increases the speed of cellular respiration.

2. It is necessary for the normal growth of the body particularly for the development of bones, hair etc.

3. The normal functions of reproductive organs depend on the activeness of thyroid gland.

4. It controls the water balance of the body in coordination with the hormones of pituitary gland.

5. Thyroxine controls the metabolic rate of body.

Diseases Caused by the Deficiency of Thyroxin

1. Cretinism: This disease affects the children. The mental and physical retardness of the child.

2. Myxedema: In this disease which normally found in youth the metabolism does not take place properly which causes reduction in heart beat and blood pressure.

3. Hypothyroidism: This disease is caused due to chronic deficiency of thyroxin hormone. Due to this disease normal reproduction is not possible. Sometimes due to its deficiency, human becomes dumb and deaf.

4. Goitre: This disease is caused by the deficiency of iodine in food. In this disease the shape of the thyroid gland enlarges abnormally. Iodization of salt in a public health measure is to prevent goitre.

Disease Caused by the Excessiveness of Thyroxin

Exophthalmic Goitre: In this disease eyes get bulging out of the eye socket with increased metabolic rate.

3. Parathyroid Gland

This is situated in the right back of the thyroid gland of the throat.

Two hormones are secreted by it:

(a) Parathyroid hormone: This hormone is secreted when there is a deficiency of calcium in the blood. It regulates the level of calcium in blood.

(b) Calcitonin: This hormone is released when there is excess of calcium in the blood. Hence, hormone secreted by parathyroid gland controls the quantity of calcium in blood.

4. Adrenal Gland

There are two parts of this gland:

(a) Outer part is cortex

(b) Inner part is medulla.

Hormones Secreted by Cortex and Their Function

1. Glucocorticoids: This controls the metabolism of carbohydrate, protein and fat.

2. Mineralocorticoids: Its main function is reabsorption of ion by kidney ducts and to control the quantity of other ion in the body.

Note:

1. Cortex is essential for life. If this is extracted completely from the body, human will remain alive only for a week or two.

2. In case of deformation of cortex, the process of metabolism gets disturbed; this disease is called Addison's disease.

Hormones Secreted by Medulla and Their Function

(a) Adrenaline (Epinephrine): This is an amino acid.

(b) Nor-adrenaline (Nor-epinephrine): This is also an amino acid.

Both the hormones are secreted in response to stress. The function of both the hormones is similar. These equally increase the relaxation and contraction of heart muscles.

As a result, blood pressure increases and decreases. In case of sudden stop of heart beat, epinephrine is helpful in re-starting the heart beat.

The hormone Adrenaline (epinephrine) increases the heart beat in mammal. The hormone secreted by Adrenal gland is called fight, flight, fright hormone known as emergency hormone.

Thymus is endocrine gland found situated in chest cavity producing the hormone thymosin. It plays a major role in the differentiation of T-lymphocytes. Thymus degenerates in old individuals resulting immune response becomes weak.

5. Gonads

(i) Ovary

The following hormones are secreted by this:

(a) Estrogen: It completes the development of reproductive organs.

(b) Progesterone: It stimulates the thickening of uterus lining during ovarian cycle.

(c) Relaxin: During pregnancy it is found in uterus and placenta. This hormone smoothens the pubic symphysis and it widens the uterine cervix so that a child is delivered easily.

Oxytocin is a hormone which helps in contraction of uterine wall during child birth and plays an important role in release of milk from mammary gland, secreted by hypothalamus produced and released by the posterior pituitary.

(ii) Testis

• The hormone secreted by it is called testosterone. It motivates the sexual behaviour and growth of secondary sexual characters. Sertoli cells are found in testis.

• The mechanism of action of oral contraceptive pills is to inhibit the release of egg.

Notes

1. Primary function of eccrine glands is to produce sweat.

2. Sweating or perspiration is nature's way of lowering the internal temperature of the body.

3. Sweat glands are present in skin.

4. When exposed to sunlight our skin gets darker due to presence of melanin.

Respiratory System

The most important organ of the respiratory system of human is lungs where the exchange of gases takes place. All those organs that help in exchange of gases are — Nasal passage, Pharynx, Larynx or Voice box, Trachea, Bronchi, Bronchioles and Lungs.

1. Nasal Passage

• Its main function is related to sniffing. Its inner cavity is lined with mucous membrane.

• This secretes approximately ½ litre of mucous every day.

• This prevents the particles of dust, bacteria or other small micro-organisms from entering into the body.

• It makes the air wet entering into the body and equalises it with the temperature of the body.

2. Pharynx

• It is situated behind the nasal cavity and is a common passage for both respiratory and digestive systems.

3. Larynx

• Pharynx opens into anterior wider part of trachea called larynx. The opening is called glottis.

• A cartilaginous flap-like structure covers the glottis called epiglottis which prevents the entry of food during swallowing.

• A pair of vocal cords is present inside the larynx which help in producing sound.

4. Trachea

• From the base of larynx a tube arises, passes through the neck and reaches up to middle of thorax called trachea.

• It is supported by ‘C’-shaped cartilaginous rings.

• Internally trachea is lined by ciliated and mucus secreting epithelium.

5. Bronchi

• In the thoracic region trachea divides into two branches called bronchi.

• Each bronchus enters into the lung of its own side. After entering into the lung, bronchus of each side divides and re-divides into very fine tubes called bronchioles.

• Finally, bronchioles give rise to alveoli or alveolar sacs.

• Alveoli are the site of gaseous exchange.

6. Lungs

• There is a pair of lungs in the thoracic cavity. Its colour is pink, red and spongy.

• Right lung is larger in comparison to left lung.

• Each lung is surrounded by a membrane which is called pleural membrane.

• There is a network of blood capillaries. Here Oxygen enters into the blood and CO₂ releases out from blood.

The Process of Respiration

The process of respiration can be divided into four parts:

1. External respiration

2. Transportation of gases

3. Internal respiration

4. Cellular respiration

1. External Respiration

This is divided into two parts:

(a) Breathing

(b) Exchange of gases

(a) Breathing

• In lungs air is taken and given out at a certain rate; this is called breathing.

• An adult breathes approximately 12 to 16 times in a minute.

Mechanism of Breathing

(i) Inspiration:

• At this stage, air from the environment enters into the lungs through the nasal passage, due to increase in the dimension of thoracic cavity.

• A low pressure is generated in the lungs and air enters into the lungs from environment. Air continues to enter until the pressure of air inside and outside the body become equal.

• Diaphragm is flattened during inspiration by its downward movement.

(ii) Expiration:

In this process, air comes out of the lungs by relaxing the diaphragm.

Constitution of Air in Breathing

Gas	Air Inhaled	Air Exhaled
Nitrogen	79%	79%
Oxygen	21%	17%
Carbon dioxide	0.03%	0.09%

Everyday approximately 400 ml water is excreted out through breathing.

The maximum volume of air which can be inhaled by human is called total lung capacity.

(b) Exchange of Gases

• The exchange of gases takes place inside the lungs.

• This gaseous exchange takes place on the basis of concentration gradient through normal diffusion.

• The exchange of oxygen and carbon dioxide gases takes place due to their difference in partial pressures. The direction of diffusion occurs on both sides.

• Diaphragm is arched during normal expiration.

• Hiccups in humans generally occur due to the forceful downward shifting of the diaphragm.

• The upper part of the respiratory tract is provided with small hair-like structures called cilia.

2. Transportation of Gases

The process of reaching of gases (oxygen and carbon dioxide) from lungs to the cells of body and coming back again to the lungs is called the transportation of gases.

• Transportation of oxygen takes place by haemoglobin present in blood.

• Transportation of carbon dioxide from cells to lungs takes place by haemoglobin only to the extent of 10 to 20% in the form of carboxyhemoglobin.

Transportation of Carbon Dioxide takes place in the following ways:

(a) By mixing with plasma:

• Carbon dioxide forms carbonic acid after mixing in plasma.

• Transportation of 7% carbon dioxide takes place in this form.

(b) In the form of bicarbonates:

• 70% part of carbon dioxide in the form of bicarbonates is transported.

• It combines with potassium and sodium of blood and forms potassium bicarbonate and sodium bicarbonate.

3. Internal Respiration

• Inside the body, gaseous exchange takes place between blood and tissue fluid which is called internal respiration.

• Note: The gaseous exchange in lungs is called external respiration.

4. Cellular Respiration

• Glucose is oxidised by oxygen reached into the cell. This process is called cellular respiration.

Types of Cellular Respiration

There are two types of respiration:

(a) Anaerobic respiration

(b) Aerobic respiration

(a) Anaerobic Respiration

• If the oxidation of food takes place in absence of oxygen. During this, only 2 ATP molecules are produced from one molecule of glucose.

• Final product of anaerobic respiration in animal tissue like skeletal muscle cell is lactic acid.

Equation:

C₆H₁₂O₆ → 2C₃H₆O₃ + Energy (in animal) (Lactic acid)

In yeast and certain bacteria ethyl alcohol (ethanol) is produced.

Equation:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy (in plant) (Ethyl alcohol)

A sprinter feels cramps and pain in the thigh muscles after a run. This is due to accumulation of lactic acid.

(b) Aerobic Respiration

• It takes place in the presence of oxygen.

• The complete oxidation of glucose takes place. As a result CO₂ and H₂O are formed and energy is released in huge amount.

Equation:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 2870 kJ energy (38 ATP)

The Complex Process in Cellular Respiration is Divided into Two Parts

1. Glycolysis (Cytoplasm)

2. Kreb’s Cycle (Mitochondria)

1. Glycolysis

• Its study was first done by Embden Meyerhof, therefore it is also called EMP Pathway.

• Glycolysis is present in both types of respiration – aerobic and anaerobic.

• This process takes place in cytoplasm.

• Breaking down of glucose in cytoplasm results in the formation of two molecules of pyruvate and energy.

• To start the process of glycolysis two molecules of ATP (Adenosine Triphosphate) are utilised.

• At the end of the process, 4 molecules of ATP are obtained. Therefore, as a result of glycolysis, 2 ATP are obtained and 14400 calories (2 × 7200 calories) energy is released.

• There is no need of oxygen in glycolysis; hence this process is similar in both anaerobic and aerobic respiration.

• In this process four atoms of hydrogen are formed which are used in converting NAD to 2NADH₂.

• The enzymes which take part in glycolysis during respiration are found in cell cytoplasm.

2. Kreb’s Cycle

• It was described by Hans Krebs in 1937.

• This is also called Citric Acid Cycle or Tricarboxylic Acid (TCA) Cycle.

• This process is completed inside the mitochondria in presence of specific enzymes.

• Breakdown of pyruvate into CO₂, H₂O and energy takes place in mitochondria. Two molecules of each ADP and ATP are formed.

• In this cycle, 4 pairs of hydrogen atoms are released.

• In complete cycle, two molecules of pyruvic acid produce 12 molecules of carbon dioxide.

• In our system, maximum number of ATP molecules are formed during Kreb’s Cycle.

Production of Energy:

• By the oxidation of pyruvic acid, one molecule of ATP, five molecules of NADH and one molecule of FADH₂ are formed.

• From one molecule of NADH – three molecules of ATP and from one molecule of FADH₂ – two molecules of ATP are obtained.

• Hence, from one molecule of pyruvic acid:

1 + (3×5) + (2×1) = 18 molecules of ATP are formed.

• From one molecule of glucose, two molecules of pyruvic acid are formed, by which 36 molecules of ATP are released.

• During glycolysis, two molecules of ATP are obtained.

• Hence, during oxidation of one molecule of glucose total 2 + 36 = 38 ATP molecules are obtained.

Respiratory Substances

Carbohydrate, fat and protein are the main respiratory substances.

• At first, oxidation of glucose takes place, then fat.

• After the consumption of carbohydrate and fat, oxidation of protein starts if energy is required.

Note:

• Respiration is a Catabolic Process.

• It also reduces the weight of the body.

• Respiration is controlled by medulla oblongata.

• Cyanide poisoning causes death in seconds due to breaking down the electron transport chain system.

• Eustachian tube helps in equalising the pressure on either side of ear drum.

• Retina of eye processes the information gathered by photoreceptor cells and sends it to the brain to decide what the picture is.

• The part of eye which is responsible for the conversion of image of an object into neural signal is optic nerve.

Final Thoughts

The human body performs vital functions through different systems working in coordination. The digestive system breaks down food into simpler forms for absorption and energy. The circulatory system transports oxygen, nutrients, and hormones through blood, while the lymphatic system helps in immunity. The excretory system removes metabolic wastes through kidneys, lungs, skin, and liver.

The nervous system controls body activities and responses through the brain, spinal cord, and nerves. The skeletal system gives shape, protection, and support to the body, while the endocrine glands regulate various functions by secreting hormones.

The respiratory system enables gaseous exchange essential for energy production. Together, these systems maintain balance and ensure proper functioning of the body.