Excretory Products And Their Elimination

Made By

J.Janani

11-A

The Excretory System

The excretory system is a biological system that removes excess, unnecessary or dangerous materials from an organism. It is responsible for the elimination of oxygen waste products of metabolism as well as other nitrogeneous materials.

Human Excretory System

Pair of kidneys

One pair of ureters

A urinary bladder

A urethra

A Pair Of Kidneys

Kidneys are reddish brown, bean shaped structures situated between the levels of last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity.

The Excretory System

Towards the centre of the inner concave surface of the kidney is a notch called hilum through which ureter, blood vessels and nerves enter.Inner to the hilum is a broad funnel shaped space called the renal pelvis with projections called calyces.Inside the kidney, there are two zones, an outer cortex and an inner medulla.The cortex extends in between medullary pyramids as renal columns called ‘columns of bertini’.

Longitudinal Section Of Kidney

The Excretory SystemEach kidney has nearly one million complex tubular structures called ‘nephrons’,which are the functional units.Each nephron has two parts

1.glomerulus

2.renal tubule.

Glomerulus is a tuft of capillaries formed by the afferent arteriole.The renal tubule begins with a double walled cup-like structure called ‘Bowman’s capsule’,which encloses the glomerulus.

Nephron

The Excretory SystemNephron is the basic structural and functional unit of the kidney. Its chief function is to

1.regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine.

2. A nephron eliminates wastes from the body,

3. controls levels of electrolytes and metabolites

4. regulates blood pH.

Malpighian Body

The renal tubule begins with a double walled cup-like structure called bowman’s capsule, which encloses the glomerulus.Glomerulus along with bowman’s capsule is,called the malpighian body.

Henle’s loop

In the kidney, the loop of Henle is the portion of the nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. The loop has a hairpin bend in the renal medulla. The main function of this structure is to create a concentration gradient in the medulla of the kidney. By means of a countercurrent multiplier system, which utilizes sodium pumps, it creates an area of high sodium concentration deep in the medulla, near the collecting duct. Water present in the filtrate in the collecting duct flows through aquaporin channels out of the collecting duct, moving passively down its concentration gradient. This process reabsorbs water and creates a concentrated urine for excretion.

TYPES OF NEPHRON

co rtica l n e ph ro nsT h e lo o p o f h e n le is to o sh ort an d ex ten d s o n ly ve ry litt le in to th e m e du lla .

ju x ta m e du lla ryT h e lo op o f h en le is ve ry lo n g a nd run s d e ep in to th m e du lla .

N e ph ron

URINE FORMATION

Urine formation involves three main processes namely-

Glomerular Filtration

Reabsorption

Secretion

Urine Formation

Urine formation involves filtration of blood, which is carried out by glomerulus and is called glomerular filtration.The glomerular capillary blood pressure causes filtration of blood through 3 layers-

1. The endothelium of glomerular blood vessels2. The epithelium of Bowman’s capsule3. Basement membrane between these two layers

Blood is filtered so finely so finely through membranes, that almost all the constituents of plasma except the proteins pass onto the lumen of the Bowman’s capsule.Therefore, it is considered as a process of ultra filtration. In physiology, reabsorption or tubular reabsorption is the flow of glomerular filtrate from the proximal tubule of the nephron into the peritubular capillaries. This happens as a result of sodium transport from the lumen into the blood by the Na+/K+ ATPase in the basolateral membrane of the epithelial cells. Thus, the glomerular filtrate becomes more concentrated, which is one of the steps in forming urine.

Reabsorption and Secretion of nephron

Nephron and vasa recta

Proximal Convoluted Tubule(PCT)

The proximal tubule is the portion of the duct system of the nephron leading from Bowman's capsule to the loop of Henle.The proximal tubule regulates the pH of the filtrate by exchanging hydrogen ions in the interstitium for bicarbonate ions in the filtrate; furthermore, it is responsible for secreting organic acids, such as creatinine and other bases, into the filtrate.