What is the difference between.....

Excretion is removal of nitrogenous wastes 

Defecation is removal of undigested waste

Types of nitrogenous wastes

AMMONIA

Some living beings waste in the form of  ammonia.Ammonia is highly toxic.These organisms are known as ammoniotelic.Examples- Sponges, coelenterates and bony fishes. 

URIC ACID

Some living organisms release waste in the form of uric acid.uric acid is least toxic.These organisms are called uricotelic.Examples- insects, reptiles and birds.

UREA

Some living organisms release waste in the form of urea.Urea is neutral and less toxic.These organisms are called ureotelic.Examples- desert mammals, cartilageous fishes and humans

Excretory organs in humans....Make a Guess

EXCRETORY SYSTEM IN HUMANS

• The excretory system or the urinary system consists ofa pair of kidneys

• a pair of ureters• urinary bladder• urethra

Location of the Kidney-In the abdominal cavity below the stomach, on either side of the vertebral column.The right kidney is placed slightly lower than the left kidney as it is pushed down by the large right liver lobe.

Blood vessels entering and leaving the kidney

The descending aorta branches to form the renal artery that enters the kidney, and the renal vein comes out of the kidney to join the inferior vena cava.

Kidneys are bean shaped structures about 10 cm long. The outer side is convex and the inner margin is concave. In the middle of the concave side a notch is present through which structures enter and leave the kidney. This is called Hilum.

Other Parts of the Urinary System

URETER10-12 inches length, half an inch diameter. 

Enters the bladder through oblique tunnels that function as valves.Carries urine from kidney to the urinary bladder. 

URINARY BLADDERPear shaped highly distensible sac-like reservoir, store urine temporarily.

Present in the pelvic region 

Opening to the urethra is guarded by sphincter muscles. 

Can hold about 0.5 to 1liter of urine. 

URETHRANarrow tube from bladder to the exterior. 

Sphincters control the urination.  Female it is 3-4 cm long and males 18- 20 cm long.

Internal Structure of the kidney

Two distinct regions are seen-Cortex- Outer dark region has a dotted appearance. 

Medulla- Pale inner region has pyramid like structures .

The pyramids open into small tube like structures the minor calyx and two or three minor calyx opens into the a major calyx.

The all the major calyces opens into the pelvis. 

The pelvis is the proximal end of the ureter that receives the urine from the calyces.

Structure of the Kidney Tubule

• Each kidney is made up of microscopic, coiled tube like units called nephrons or uriniferous tubules.• There are approximately 1.25 to 1.5 million nephrons in one kidney.1. The nephron has two parts-

A cup shaped body called Malpighian corpuscle or Renal corpuscle.

2. A tubular part called renal tubule.Questions:

1. What gives Cortex its dotted appearance?

2. What gives Medulla a Striated appearance?

PARTS OF THE NEPHRON

• Branches of the renal artery within the kidney produce afferent arterioles.• Each afferent arteriole leads to a network of capillaries called a glomerulus.• Blood leaves the capillaries of the glomerulus via an efferent arteriole and enters capillaries in the medulla called peritubular capillaries, which collect much of the water that was lost through the glomerulus.Venules from the peritubular capillaries lead to the renal vein, which exits the kidney and returns blood to the inferior vena cava.

RENAL TUBULE The tubular part of the nephron is known as renal tubule. It has three parts- Proximal convoluted tubule, Loop of Henle and distal convoluted tubule.

The proximal part of the renal tubule is highly coiled and is present in the renal cortex. This part absorbs water and all the useful salts, amino acids and glucose.The proximal part extends downwards to form a narrow tubular part- the descending part, a loop and an ascending part. This lies in the medulla and mainly absorbs water from the nephric filtrate.

The ascending limb leads to a convoluted part the which also lies in the cortex. This opens into the collecting tubule. This part excretes some ions and ammonia into the filtrate.

Try this link to lead yourself to a pretty good animation explaining the process.Http://www.biologymad.com/resources/kidney.swf

Urine FormationINVOLVES THREE PROCESSES: 

ULTRAFILTRATION.- Filtration under high pressure. Bowman's capsule acts as ultra-filters. When blood flows through glomerular capillaries- all substances (except blood cells and plasma proteins) are filtered. Main reason for ultrafiltration is the difference in the size of afferent and efferent arterioles. The efferent arteriole are narrower than the afferent arteriole.

TUBULAR REABSORPTION.- absorption of useful substances from the nephric filtrate into the blood. (diffusion and active transport) 

TUBULAR SECRETION.- secretion of harmful substances from the blood into the nephric filtrate by the cells of DCT

Urine Formation cont.

Steps of Urine Formation

•Ultrafiltration

Glomerulus

•Receives glomerular Filtrate

BOWMAN’S CAPSULE

•Re-absorbs most water about 2/3, and much of glucose/Na+ / Cl ion.

PCT

•Some absorption of water and Na+

LOOP OF HENLE

•Reabsorption of remaining water and Chlorides.

•Walls secrete K+ and foreign chemicals such as penicillin and other drugus into the forming urine

DCT

Role of Hormones in Urine Formation

ADH- Anti Diuretic Hormone, Diuresis means increased production of urine• Results in reabsorption in collecting tubule• Secreted by posterior pituitary gland• It is released in response to high blood Osmolarity.• Increased osmolarity results from water loss and dehydration, thus body needs to retain more water.• ADH allows water to be reabsorbed from collecting tubule and not leave the body.• Water is absorbed by osmosis due to high Medullary hypertonicity. • Lack of ADH causes large amount of dilute urine. A condition called diabetes insipidus.• Question: Why during workout you are suggested to drink limewater instead of plain water?

Reabsorption of NaCl from the distal convoluted tubule is controlled by aldosterone from the adrenal cortex. One of a group of hormones from theadrenal cortex called mineralcorticoids which regulate salt levels in the body.

Constituents of UrineOrganic Gm/L Inorganic Gm/L

Urea 2.3 NaCl 9.0

Creatinine 1.5 KCl 2.5

Uric Acid 0.7 Ammonia 0.6

Others 2.6 Others 2.5

• Mainly Urine consists of about 95% WATER and 5% of SOLID wastes dissolved in it.• Abnormal Constituents in urine 1. Blood Cells- Blood passing thru’ Urine due to infection or kidney

stone or tumor.2. Glucose/Glycosuria – Excess glucose passing through urine due to

DIABETES MELLITUS. 3. Albumin – Due to high BP or bacterial infection permeability of

Bowman’s Capsule membrane increases.4. Bile Pigments- Anemia, Hepatitis (jaundice) or liver cirrhosis.

References

• Tges Biology Dept• Science direct• www.nature.com