Zoology Assignment Help >> Structure & Functions of Kidney, Pancreas, Lungs, Testes, Ovaries, Histology

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KIDNEY

1. Each kidney is bean shaped structure; 11 cm long, 6 cm broad and 3 cm thick in man

2. Left kidney is little longer and narrower.

3. Kidneys are retro-peritoneal organs.

4. Foetal kidney is 12 lobuled and in adult lobules fuse and kidney becomes smooth.

5. Right kidney is slightly lower than left.

6. The concavity of kidney is called hilus.

7. Hilus leads into renal sinus within the kidney.

8. Renal pelvis divides into 2-3 major calyces and they in turn into 7-13 minor calyces.

9. Renal papillae are the nipple like projection from the wall of the renal sinus and represent the apices of renal pyramids.

10. Capsule of kidney called renal capsule is made up of three layers. These are from outside to inside.

(i) Renal fascia (fascia of gerota).

(ii) Perirenal fat or perinephric fat.

(iii) Fibrous capsule made up of white fibres with a few yellow and smooth muscles.

11. Each kidney is composed of 1-3 millions of uriniferous tubules or nephrons. These are functional units of kidney. All nephrons do not function at the same time.

12. Nephron is exactly the secretory part of uriniferous tubule while other part is the collecting tubule.

13. Anatomically kidney is having two areas=outer cortical region called cortex and inner medullary region called medulla.

14. Cortex extends into medulla and divides it into many pyramids, about a dozen in human and single in rabbit. These extension of cortex are called the renal columns of Bertini.

15. Nephron is composed of-

(i) Renal corpuscle or malpighian corpuscle- This is made up of glomerulus and Bowman's capsule.

(ii) Renal tubule-For selective reabsorption and comprises proximal convoluted tubule, loop of Henle and distal convoluted tubule.

16. Collecting tubule arises from distal convoluted tubule. Many collecting tubule combines and form ducts of Bellini.

17. Descending and ascending limbs of loop of Henle and parts of collecting tubule are found in medullary ray while proximal and distal convoluted tubule and junctional tubule are found in cortex.

18. Near the junction of ascending limb of loop of Henle and distal convoluted tubule, the juxta glomerular apparatus is found. It is formed by-

(i) Macula densa

(ii) Juxta glomerular cells

(iii) Polkissen cells

It is supposed to secrete renin hormone which causes arterial constriction.

PANCREAS

Pancreas is a double gland being partly exocrine and partly endocrine. Exocrine part secretes:" digestive pancreatic juices and endocrine part secretes hormone like insulin. It is a soft, lobulated and elongated gland. It is "J" shaped and of about 6-8 cm in length. Its weight is about 90 grams in man. It is pinkish to red in colour. It is the second largest gland of the body.

(1) Exocrine part - Pancreas is covered by two layers forming capsule.

These are -

(i) Outer-Serous capsule of peritoneum.

(ii) Inner-Internal capsule of connective tissue.

The exocrine part is a serous gland which is made up of tubular acini lined by pyramidal cells. These acini are embedded in the connective tissue having blood vessels, nerve fibres, smooth muscle fibres and the mast cells. Lobular walls are single layered and single cell thick. The cells are typically zymogenic and their cavity continues in the duct of the acini. Several acinar ducts join and form interlobular duct. Several not all, interlobular ducts join and form larger panceratic duct which is also called as duct of Wirsung. Before opening in the second part of duodenum, it combines with the bile duct and form hepato-pancreatic ampullae.

Another accessory pancreatic duct is also found. It is called accessory pancreatic duct or duct of Santorini.

(2) Endocrine part: It is formed by the islets of Langerhans distributed as small isolated mass throughout the pancreas. Adult human pancreas contains about 2,00,000 to 17,00,000 islets. They are yellowish brown in colour. Each is having a rich supply of blood. Each islet is made up of following cell types-

(i) a or A cells-Sub-types are A, or D cells and A2 cells. These cells are granular and acidophillic. They form about 20% of total cell population of the endocrine part. A, cells belong to the enterochromaffin group and are supposed to secret pancreatic gastrin and the serotonin. A2 cells secret only glucagon

(b) ß or B cells-They are granular and basophillic in nature.

They are most numerous and form about 80% of total cell population of the endocrine part. They secret insulin hormone.

(iii) C, F and X cells-Their existence and function are doubtful in man.

Functions of pancreas:

(1) Digestive-Pancreatic juice contains many digestive enzymes which play a vital role in digestion of proteins and lipids. Some enzymes are -

(a) Trypsin-Protein digesting enzyme.

(b) Amylase-Carbohydrate digesting enzyme.

(c) Upase-Lipid digesting enzyme.

(2) Pancreatic juice provides appropriate alkaline medium (pH=8) for the proper activity of pancreatic enzymes.

(3) Endocrine function will be described later.

LUNGS (PULMONES)

The lungs are a pair of respiratory organs situated in the pleural cavity separated by mediastinum. Each lung is conical in shape, black to brown in colour and spongy in texture. Right lung is heavier than left. Lungs in foetus or stillborn are solid and sink in water.

The right lung is divided into three parts by two fissures (oblique and horizontal). These three parts are superior, middle and inferior lobes. The left lung is divided by only oblique fissure into only two parts. These are upper lobe and lower lobe. The tongue shaped projection of left lobe below the cardiac notch is called lingula which represents the middle lobe morphologically. Sometimes right lung may have two to five lobes. Additional lobes are infracardiac lobes for azygous vein. The left lobe can have one to three lobes.

Each lung is covered by a capsule formed by an outer serous coat of the simple squamous epithelium. This is also called mesothelium and inner sub-serous layer called lamina propria made up of connective tissue. This layer extends inwards into the lungs and divides it into many polyhedral lobules. Each lobule again divides into many air sacs.

Bronchial tree-The trachea divides into two principle or primary bronchi, one for each lung. The right bronchus is wider and the left bronchus is narrow and more oblique

Each bronchus enters lungs through hilus and divides into secondary or lobar bronchi, one for each lobe of lungs. Each lobe divides into tertiary or segmental bronchi. The segmental bronchi divides repeatedly into very small branches called terminal bronchioles which loose oartilage to become respiratory bronchioles. Each respiratory bronchiole divides into 2-11 alveolar ducts. Each duct divides into air passages called atrium. The atria ends in air saccules or alveoli.

Respiratory unit-It is a small part of lung aerated by respiratory bronchioles. It consists of-

1. Respiratory bronchiolels

2. Alveolar ducts

3. Atrium

4. Air saccules

5. Pulmonary alveoli.

The gaseous exchange takes place in the alveoli. They are lined by flattened epithelium.

TESTES

Testis are the male reproductive organ homologous to ovary of female. Testis is oval in shape and in adult they are of about 10-15 grams each. In foetal life they are in abdominal cavity while at the time of birth they descend down to scrotum. The left testis is slightly lower than right. The failure of descend results in testes being retained somewhere in the route of descend. This condition is called as cryptorchidism. e.g. testes in elephant.

From outside inwards the three coats of testis are-tunica vagina/is, tunica albuginea and tunica vesculosa.

(1) Tunica vaginalis - It has a parietal and visceral layer and a cavity in between these two. It covers whole of the testis except its posterior surface. The sinus of epididymus is a part of this cavity.

(2) Tunica albuginea - It is white fibrous coat covering the testis all around. The posterior border of this is thickened to form an incomplete vertical septum called "mediastinum testis". Numerous septa called saptula testis extend from mediastinum to the inner surface of the tunica albuginea which completely divides the testis into the 200-300 lobules.

(3) Tunica vasculosa - It is the inner vascular layer of testis, lining its lobules.

Each lobule is made up of about 2-3 seminiferous tubules and interstitial cells in between. Seminiferous tubules combine and form straight tubules which again combine and form rete testis. Rete testis join up and form vasa efferentia which finally combine to form the duct of epididymus. At the back of testis the epididymus continues as vas deferens.

Each tubule is composed of two types of cells-

1. Spermatogenic cells

2. Supporting cells or subtentacular cells.

Spermatogenic cells are found in various stages of development viz. sperm mother cell, spermatogonia, spermatocytes (primary and secondary), spermatids and finally sperms.

Supporting cells are also called cells of sertoli. They are tall and columnar in shape. They protect, support and nourish the developing germ cells.

The cells of Leydig are found in small clusters in between seminiferous tubules. They are supposed to secrete hormones testosterone and in small quantities oestrogen.

The release of spermatozoa from the cells of sertoli is called spermiation.

OVARIES

Ovaries are a pair of female reproductive organ lying in the pelvis. They are almond shaped and greyish pink in colour. Ovary is having almost six components-

(1) Germinal epithelium-It is the outermost covering of a single layer of cuboidal cells. It is continuous with coelomic epithelium. Graafian follicle develops from this layer.

(2) Tunica albuginea-It is a thin layer of eosinophillic collagenous connective tissue.

(3) Stroma - Its cells are spindle shaped. It is composed of connective tissue and smooth muscle fibres. It provides support to essential ovarian tissue and carries blood vessels, lymphatics and nerves. It is called medulla.

(4) Vesicular follicles-These are also called Graafian follicles. They develop from parent germinal epithelium. They are scattered mostly in the peripheral part of the ovary. In the centre ovum being surrounded by a layer of other cells. Area in which the Graafian follicles are situated is called cortex.

The number of oocytes per ovary reduces much from intra-uterine life to adulthood. Only about 400 oocytes are liberated by both ovaries in a woman during her entire reproductive life of about 30 years.

(5) Corpus luteum - When the graafian follicle ruptures, corpus luteum develops of the remainants of the ruptured follicle. The corpus luteum acts as a temporary endocrine gland and secretes hormone progesterone.

(6) Interstitial cells-These are groups of polyhedral cells containing lipid granules representing stored active principle. They develop from the stroma cells or unruptured follicles. They probably secrete oestrogen.

Structure of graafian follicle: There is no maturation of follicles in childhood. After childhood, maturation begins and proceed to some extent and then follicle degenerate. They are called atretic follicles. At puberty, matruation is complete. At each menstural cycle, only one ovum matures and discharged.

Graafian follicle is having a cavity called follicular cavity or antrum. Cavity is surrounded by two layers

(1) Peripheral-Membrana granulosa.

(2) Central-Discus proligerus or cumulus oophoricus or cumulus ovaricus. The innermost cells are disposed from cumulus about the ovum in radial fashion. They form corona radiata.