Zoology

System of the Human Body

By Examguru / 22 May, 2023 / Download PDF

System of the Human Body

(A) Digestive System

The complete process of nutrition is divided into five stags :

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 convert starch into simple sugar and make 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 reach 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.

Digestion in Stomach

  • The foods lies approximately for four hours in stomach.
  • After reaching the food in stomach gastric glands secretes the gastric juice. This is a light yellow acidic liquid.
  • pH of gastric juice is about 1.5 to 3.5.
  • 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 amylase reaction of the saliva end.
  • 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.

Digestion in Intestine

Intestine is divided into two main parts: (a) Small intestine (b) Large intestine.

(a) Small intestine:

It is sub divided into three parts

Duodenum, Jejunum and Ileum.

Note: First enzyme which mix 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.
    i.
    Trypsin: It converts the protein and peptone into polypeptides and amino acid.
    ii.
    Amylase: It converts the starch into soluble sugar.
    iii.
    Lipase: It converts the emulsified fats into glycerol and fatty acids.
  • Cholecystokinin is a harmone secreted by endocrine cells of duodenum which induce 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 completed and absorption of digested foods start.
  • From the wall of small intestine, intestinal juices secrete.

The following enzymes contain:

  1. Erespsin: It converts the remaining protein and peptone into amino acids.
  2. Maltase: It converts the maltose into glucose.
  3. Sucrase: It converts the sucrose into glucose and fructose.
  4. Lactase: It converts the lactose into glucose and galactose.
  5. Lipase: It converts the emulsified fats into glycerol and fatty acids.

Intestinal juice is alkaline in nature.

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

Ileum

  • The ileum is the final section of the small intestine in vertebrates. It comes after the jejunum and connects with the cecum of the large intestine.
  • Structurally, the ileum contains similar tissue layers as the rest of the small intestine but the diameter is slightly smaller at about 2-3 cm. The inside surface has folds called plicae circulares and projections called villi to maximize absorption.
  • The primary functions of the ileum are the absorption of vitamin B12, bile salts and any remaining nutrients from digested food that were not absorbed in the duodenum or jejunum sections before it. This includes absorption of fatty acids, amino acids, and carbohydrates.
  • The ileum is also where bile produced in the liver is excreted into the small intestine to help emulsify fats. Additionally, the Peyer's patches found in the ileum's mucosa play an important role in the immune system by monitoring intestinal bacteria.
  • In the human body, the ileum is located in the lower right quadrant of the abdomen, between the jejunum and the cecum of the large intestine. It measures around 2–4 meters long in adults.
  • Some key diseases related to the ileum include Crohn's disease which causes inflammation, celiac disease impacting vitamin absorption, and ileus in which the muscles fail to work properly impacting food transit.

3. Absorption:

Digested food get mixed into blood is called absorption.

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

4. Assimilation:

Use of absorbed food in the body is called assimilation.

(b) 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 ceaccum.
  • Digestion of food is completed in small intestine.
  • Complete digestion of fat takes place in small intestine.
  • Small intestine is longer than the larger intestine.

Summary of Digestion

S.

Gland juice

 

Enzyme

Common Name

Scientific Name

1.

Saliva

(i)

Amylase

Starch

Maltose

2.

Gastric Juice

(ii)

Pepsin

Protein

Peptones

(iii)

Rennin

Casein

Calcium paracasein

3.

Pancreatic juice

(i)

Trypsin

Protein

Polypeptides

(ii)

Amylase

Starch

Sugar

(iii)

Lipase

Fat

Fattyacid & glycerol

4.

Intestinal juice

(i)

Erepsin

Protein

Amino acid

(ii)

Maltase

Maltose

Glucose

(iii)

Lactase

––

Glucose & fructose

(iv)

Sucrase

––

Glucose & 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 accelerate the action on enzymes present in the intestine.
  • Liver convert 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 converts some quantity of protein into glucose during deficiency of carbohydrate.
  • In carbohydrates metabolism liver converts the excess of glucose found in blood into glycogen and stores it into hepatic cell as reserve nutrient. If the necessity of glucose arise the liver convert glycogen into glucose. Thus, it regulates the quantity of glucose in the blood.
  • In case of decrease of fat in food liver converts some of the 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 prohibit the clotting of blood inside the body.
  • The dead RBC is destroyed by the liver only.
  • The liver reserve some quantity of iron, copper and vitamin.
  • 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 bite coming out of liver is stored.

  • Bite 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 I 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. It makes the medium of food alkaline so that pancreatic juice can worked.

2. It kills the harmful bacteria coming with food.

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 the duct, liver cells stop taking billrubin from blood. As a result, billrubin 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 contain 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 β cell-insulin, from α cell-glucagons and from δ cell-somatostaintin hormones are secreted:

Insulin:

It is secreted by β-cell islets of Langerhans.

  • Glucagon is secreted by α-cell and somatostatin harmone is secreted by δ-cell of islets of langerhans.
  • Insulin was discovered by Fredrick Banting and Best in the year 1921.
  • It 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 loss the consciousness and visual disturbances.

Glucagon:

It re-converts 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 harmone like insulin & glucagon.

  • Malfunctioning of pancreas cause 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

i. Heart Circulatory System:

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 persist.

  • 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 carry pure blood.
  • Pulmonary vein carries the blood from lungs to left atrium. It carry pure blood. i.e., oxygenated blood.
  • The main blood vessels carrying the blood from the heart towards the body is called arota. This is the largest artery found in human.
  • Arteries carry blood from the heart to different part 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 carry 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 mean blood have to cross two time from heart before circulating throughout the body.

  • Right atrium receive impure blood from the body which goes into right ventricle. From here the blood went into pulmonary artery which carry it to the lung for purification. After purification it is collected by pulmonary vein which bring it back to heart in left atrium. From atrium it went into left ventricle. Now this purified blood is sent into aorta for different organ of body.This circulation is done is 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 the life. There is a node from which contraction of heart originated known as SA node.

1. Sinoatrial node (SA node): It is a specialized area of cardiac muscle fibre in right auricle. SA node is also known as pacemaker as it generate each wave of cardiac impulse.

2. Atrioventricular node (AV node): AV node is present close to the intertrial septum near the right AV aperture. Wave of contraction is picked up by AV node which spread through.

  • Wave of excitation is picked up by AV node which spread through AV bundle of muscles fibres present on inter arterial 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 simulate the heart electrically at regular intervals.
  • Systole and diastole of the heart are collectively called heart beat. In the normal condition the heart of the human beat 72 times 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)
  • Blood pressure is measured by sphygmomanometer.
  • Thyroxin and adrenaline are the hormones which independently controls 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 obstructed the flow of blood.

ii. Lymph Circulatory System

  • The light yellow 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 helps to prevent the body from diseases by killing the harmful bacteria or other toxic foreign bodies.

2. The node found in lymph vessels are called lymph node works as a filter or microbes in the human body.

3. Lymph helps in healing the wounds.

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

 

(C) 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 divide 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 meanings.
It is situated in a bony box called cranium which protect it from external injury.

(a) Fore Brain:

Two weight of the brain of the human is 1350 grams approx.

(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 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 some what at the back of head and consist of two cerebellar hemisphere like cerebrum. It is (Voluntary) centre for coordination of muscular body movements and maintenance of posture keeping body in balance. It is second large 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 contains 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 known the function of brain.

Spinal cord:

The posterior region of the medulla oblongata forms the spinal cord. Its main functions are:
(a) Coordination and control of reflex actions i.e. it works as the centre of the reflex actions.
(b) It carries the impulses coming out of brain.

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

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 nerve.

  • There are 12 pairs of cranial nerves and 31 pairs of spinal nerve found in a human.
  • The unit of nervous tissues is called Neuron or nerve cell.

3. Autonomic Nervous System:

Automatic 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 Automatic Nervous System :

(a) Sympathetic Nervous System

(b) Parasympathetic Nervous System.

Function s of Sympathetic Nervous System

  • It narrows the blood vessels in the skin.
  • By its action hair gets erected.
  • It reduces the secretion of salivary glands.
  • It increases the heart beat.
  • It increases the secretion of sweat glands.
  • It stretches the pupil of eye ball.
  • It relax the muscles of urinary bladder.
  • It reduces the speed of contraction & relaxation of intestine.
  • The rate of respiration increase.
  • It increases the blood pressure.
  • It increases the sugar level in the blood.
  • It increase the number of Red Blood Corpuscles in the blood.
  • It helps in clotting of blood.
  • Collective impact of this affects fear, pain and anger.

Functions of Parasympathetic Nervous System:

The function of this system is normally the opposite of Sympathetic Nervous System. For example :

  • It widens the lumen of blood vessels except the coronary blood vessels.
  • It increase the secretion of saliva and other digestive juices.
  • The contraction of pupil is caused by this.
  • It creates contraction in the other muscles of the urinary bladder.
  • It creates contraction and motion in intestinal walls.
  • The effect of this nervous system collectively creates the occasion of rest and joy.

 

(D) Respiratory System

  • The most important organ of the respiratory system of human is lungs where the exchange of gases takes place.
  • All those organs comes under respiratory system which help in exchange of gases are – Nasal passage, Pharynx, Larynx or Voice box, Trachea, Bronchi, Brochioles, Lungs etc.
  • Nasal passage: Its main function is related to sniffing. Its inner cavity is lined with mucous membrane. This secretes approximately 1⁄2 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 equalizes it with the temperature of the body.
  • Pharynx: It is situated behind the nasal cavity a common passage for both respiratory and digestive system.
  • Larynx: Pharynx open into anterior wider part of trachea called larynx. The opening is called giottis. A cartilaginous flap like structure cover the glottis called epiglottis which prevent the entry of food during swallowing. A pair of vocal cord is present inside the larynx help in producing sound.
  • Trachea: From the base of larynx a tube is arises, passes through the neck and reaches upto middle of thorax is called trachea. It is supposed by ‘C’ shaped cartilaginous ring. Internally trachea is lined by ciliated and mucus secreting epithelium.
  • 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 divide and redevide into very fine tube called bronchioles. Finally bronchioles give rise alveoli or alveolar sac. Alveoli are the site of gaseous exchange.
  • Lungs: There is a pair of lungs in the thoracic cavity. Its colour is pink, red and looks like sponge. Right lung is larger in comparison to left lung. Each lung is surrounded by membrane which is called pleural membrane. There is a network of blood capillaries. Here Oxygen enter into the blood and CO2 releases out from blood.

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:

In lungs air I taken and given out at a certain rate is called breathing. An adult breath approximately 12 to 6 times in a minute.

Mechanism of Breathing:

(i) Inspiration: At this stage, air from the environment enter into the lungs through the nasal passage, due to increases 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 became 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

 

Nitrogen

Oxygen

Carbon dioxide

The air inhaled

79%

21%

0.03%

The air exhaled

79%

17%

4%

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 human is called total lung capacity.

The exchange of oxygen and carbon dioxide gases takes place due to their difference in partial pressures. The direction of diffusion is both side.

  • Diaphragm is arched during normal expiration.
  • Hiecups in human 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 lung takes place by haemoglobin only to the extent of 10 to 20%.
  • Transportation of carbon dioxide takes place through circulation of blood :

(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 combine 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 oxidized by oxygen reached into the cell. This process is called cellular respiration.

There are two types of 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.

In yeast and certain bacteria ethyl alcohol or ethanol is produced.

(b) Aerobic respiration:

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

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 Meyorh pathway. Therefore, it is also called EMP path.

  • Glycolysis is present in both types of respiration, Aerobic and Anaerobic. This process takes place in cytoplasm.
  • As a result of decomposition of one glucose atom in glycolysis, two atoms of pyruvic acid is formed.
  • To start this process 2 atoms of ATP (Adenosine Triphosphate) takes part but at the end of process 4 atoms ATP are obtained. Therefore, as a result of glycolysis 2 atom ATP are obtained i.e. 16000 calorie (2 x 8000) energy is obtained.
  • There is no need of oxygen in glycolysis. Hence, this process is similar in both anaerobic and aerobic respiration.
  • In this, four molecules of hydrogen formed which is used in converting NAD to 2NADH2.
  • The enzyme which take part in glycolysis during respiration are found in cell cytoplasm.

2. Kreb’s Cycle:

It was described by Hens Krebs in 1937.

  • This is also called Citric Acid Cycle or Tricarboxylic Cycle.
  • This process is completed inside the Mitochondria in presence of specific enzymes.
  • Break down of pyruvate into CO2, H2O and energy takes place in mitochondria.
  • Two molecule of each ADP and ATP are formed.
  • In this cycle 4 pair of hydrogen atom are released.
  • In complete cycle tow molecule of pyruvic acid produce 12 molecule of carbondioxide.
  • In our system maximum number of ATP molecule are formed during Kreb’s Cycle.

Production of energy: By the oxidation of pyruvic acid one molecule of ATP, five molecule of NADH and one molecule of NADH2 are formed. From one molecule of NADH three molecule of ATP and from one molecule of NADH2 two molecule of ATP are obtained. Hence, from one molecule of pyruvic acid 1 + (3 x 5) + (2 x 1) = 18 molecule of ATP are formed. From one molecule of glucose, two molecule of pyruvic acid are formed, by which 36 molecule of ATP are obtained. Hence, during oxidation of one molecule of glucose total 2 + 36 = 38 ATP molecule are obtained.

Respiratory substances: Carbohydrate, fat and protein are the main respiratory substance. At first, oxidation of glucose takes place, then fat. After the consumption of carbohydrate and fat oxidation of protein start 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 second due to breaking down the electron transport chain system.
  • Eustachian tube help in equalizing the pressure on either side of ear-drum.
  • Retina of eye process the information gathered by photoreceptor cells and send it to the brain to decide what the picture is.
  • The part of eye which is responsible for the conversion of image of on object into neural signal is optic nerve.

 

(E) 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 main excretory organs of human are as follows –

1. Kidneys2. Skin,  3. Liver and  4. Lungs

1. Kidneys:

The main excretory organ in human and other mammals is a pair of kidneys. It 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 1,30,00000 kidney ducts which are called nephrons. Nephron is the structural and functional unit of the kidney. There is a cup like structure in the 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: This 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 ultra filtration.
  • The main function of the kidneys is purification of blood plasma i.e. to excrete the unwanted nitrogenous waste substances through urination.
  • The supple of blood to 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 mix 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 compound.
  • 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 body is

Kidney → Ureter → Urinary bladder → Urethra

  • Urine is acidic. It pH value is 6.
  • The stone formed in the kidneys is made up of calcium 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 lung 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.

Different Animals and Excretory parts

S.

Animal

Excretory parts

1.

Unicellular animal

By diffusion through general body surface and contractile vacoule

2.

Animals of Porifera Phylum

By general body surface

3.

Coelenterates

Directly by cell

4.

Flat worm

By flame cell

5.

Animals of Annelida Phylum

By nephridia

6.

Arthropods

By Malpighian tubules

7.

Crustaceans

Antennal gland

8.

Mollusca

By urinary organ

9.

Vertebrate

Mainly by kidneys

Hemodialysis: Process of removal of excess urea from the blood of patient using artificial kidney.

 

(F) Skeleton 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 bone and hyoid is made up of one bone.

ii. Vertebral Column:

The vertebral column of the human is made up of 33 vertebra. All the vertebra are joined together by intervertebral disc. Vertebra is made flexible by these intervertebral disc. We divide the whole vertebral column into the following parts –

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

1.

Cervical region

7 vertebras

2.

Thoracic region

12 vertebras

3.

Lumber region

5 vertebras

4.

Sacral region

(1) 5 vertebras

5.

Caudal region

(1) 4 vertebras

 

 

Total - 33

Functions of vertebral column:

  • Holds the head.
  • It provides the base to the neck and body.
  • It helps the human in standing, walking etc.
  • It provides flexibility to the neck and body by which a human can move neck and body in any direction.
  • It provides protection to spinal cord.

(b) Appendicular skeleton:

The following are the parts of it –

(i) Foot bones – Both hands and feet have 53 bones. Foot is consist of 26 bone while hand is made up of 27 bone.

(ii) 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 hindlimb is called pelvic girdle.
  • Pectoral girdle joined with forelimb is called humerus and the bone from pelvic girdle join to hindlimb is called femur.

Function 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.

  • 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 smallest 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 body parts –

Ear bones

Maleus

(2)

Incus

(2)

Stapes

(2)

Palm

Meta carpals

(10)

Thigh

Femur

(2)

Knee

Patella

(2)

Sole

Meta tarsal

(10)

Upper arm

Humerus

(2)

Fore arm

Radio ulna

(2)

Wrist

Carpals

(16)

Fingers

Phalanges

(28)

Hindlimb

Tibia fibula

(4)

Ankle

Tarsal

(14)

  • External ear of man is mainly made up of Cartilage.

Note:
1. The muscles and bones are join together by tendon.
2.
The muscle which joins bone to bone is called ligaments.

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

 

(G) Endocrine System

A. Exocrine glands:

Glands which have duct are called exocrine gland. Secretion of enzymes pass through it.
Example – Digestive gland, Sweat gland, Mucous gland, Salivary gland etc.

B. Endocrine gland:

These are ductless gland. Hormones are secreted by these gland. Hormones are sent to the different parts of the body through blood plasma.
Example – Pituitary gland, Thyroid gland, Parathyroid gland etc.

Functions and effect of the main endocrine system 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 fore head. This is called sella – turcica.

  • Its weight is approximately 0.6 grams.
  • This is also known as master gland. Pituitary gland is controlled by hypothalamus.

The functions of the hormones secreted by Pituitary gland:

I. STH Hormone (Somatotropic hormone):

It controls the growth of the body especially the growth of bones. By the excessiveness of STH gigantism and acromegaly are caused, in which height of the human grows abnormally. Lack of STH causes dwarfism in human.

II. TSH Hormone (Thyroid Stimulating Hormone):

It stimulates the thyroid gland to secrete hormone.

III. ACTH Hormone (Adrenocorticotropic Hormone):

It controls the secretion of adrenal cortex.

IV. GH Hormone (Growth Hormone):

It controls the functions of gonads. This is of two types:

(a) FSH Hormone (Follicle-Stimulating Hormone):

In male it simulates spermatogenesis in somniferous tubules of the testis. In female, it simulates the Graafian follicles of the ovary to secret the hormone Oestrogen.

(b) LH Hormone (Luteiniging Hormone): Interstitial cell simulating hormone, secretion of testosterone hormone takes place in make and in case of female estrogen hormone secreted.

V. LTH Hormone (Lactogenic Hormone):

Its main function is to stimulate secretion of milk in breasts for infants.

VI. 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.

  • 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 & regulating body temperature.
  • The hormones serotonin is know to be helpful in coping with stress.

2. Thyroid gland:

This is situated below the larynx on both side of respiratory teaches in throat of human.

  • The hormones secreted by it are Thyroxin and Triiodothyronine.
  • The harmone thyroxin contain iodine.

Function of Thyroxin:

  • It increase the speed of cellular respiration.
  • It is necessary for the normal growth of the body particularly for the development of bone, hair etc.
  • The normal functions of reproductive organs depend on the activeness of thyroid gland.
  • It control the water balance of the body in coordination with the hormones of pituitary gland.
  • Thyroxin control 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 the 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 enlarge abnormally. Iodization of salt in a public health measure is to prevent goitre.

Diseases caused by the Excessiveness of Thyroxin:

Exothalmic 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 regulate the level of calcium in blood.

(b) Calcitonin: This hormone is released when there is excess of calcium in the blood is present.

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 and
(b) Inner part is medulla.

Hormones secreted by cortex and their function –

(i) Glucocorticoids: This controls the metabolism of carbohydrate, protein and fat.

(ii) 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-adrenalinor (Nor epinephrine) – This is also an amino acid.

  • 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 secreted by Adrenal gland is called fight flight, fright, fight hormone known as emergency harmone.
  • Thymus is endocrine gland found situated I chest cavity produce the harmone thymosin. It simulates the immune system. With advancing in age its secretion decreases.

5. Gonands gland:

(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 ovarien cycle.

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

  • Oxytocin is a harmone which help in contraction of uterine wall during child birth and play an important role in release of milk from mammary gland, secreted by hypothalamus.

(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.

Note:

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 get darker due to presence of melanin.

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