Biology Excretion

What is excretion?

Process by which metabolic waste products and toxic substances are removed from the body of an organism

What is metabolism?

Sum total of all chemical reactions occuring in the cells of an organism

1. Anabolism --> metabolic reaction where simple molecules are built up into comples molecules with a net intake of energy

2. Catabolism --> complex molecules are broken down into simpler molecules with a net release of energy

What are metabolic waste products?

Metabolic waste products (e.g. Carbon dioxide) are unwanted substances from metabolic reactions

- they are harmful to the body if allowed to accumulae

- must be removed or deposited out of the body as harmless insoluble substances

What are the functions of a healthy kidney

1. Remove nitrogeneous waste products and excess water and mineral salts in the form of urine
2. Regulates salt and water balance of blood plasma
3. Maintain pH and composition of blood plasma

Parts of the urinary system

1. Hilum -- depression where renal artery, renal vein and nerves are connected to kidney

2. Kidney -- remove urea and excess water from the blood (urine) and keeps chemical concentration balanaced in the blood

3. Ureter -- narrow tube that emerges from the hilum, bring urine from the kidneys to the urinary bladder

4. Urinary bladder -- elastic, muscular bag that stores urine

5. Sphincter muscle -- controls urine flow into and out of the urethra

6. Urethra -- duct through which urine passes out of the body

Blood vessels and kidneys

Renal arteries -- oxygenated blood containing urea and excess water from heart to kidneys
Renal vein -- deoxygenayed blood (urea and water removed) from kidney to hear

Internal structure of kidney

Cortex -- outer darker red region enclosed by fibrous capsule
Medulla -- inner, thicker paler red region + contain 12-16 structures called pyramids

Pyramids project...

into the renal pelvis which is the enlarged part of the ureter inside the kidney

Nephron

basic functional units of the kidneys -- each kidney contains about a million nephrons

Parts of nephron

1. Bowman's capsule
2. Proximal convoluted tubule
3. loop of Henle
4. distal convoluted tubule

How does blood flow through the nephron?

Ultrafiltration

Occurs in glomerulus
Mechanical filtration to remove small molecules from the blood
Most of the blood plasma is forced out of glomerulus blood capillaries into the Bowman’s capsule to form glomerular filtrate

Conditions for ultrafiltration

ultrafiltration

1. High hydrostatic blood pressure in the glomerulus
- Difference in diameter between the afferent and efferent arterioles creates high hydrostatic blood pressure in glomurulus
- afferent arteriole wider than efferent arteriole
- main force for ultrafiltration
2. Partially permeable membrane
- basement membrane have small pores so only allows water and very small molecules to pass throughultrafiltration

Purpose for ultrafiltration

1. Water, mineral salts, glucose, amino acids and nitrogeneous waste products (urea) are filtered off during ultrafiltration
2. Blood cells, platelets and large molecules are not filtered

Selective reabsorption

Some subs reabsorbed from filtrate during ultrafiltration
Occurs through walls of tubule into surrounding blood capillaires

Parts involved (tubule) with selective reabsorption

What happens to the rest of the waste products after going through selective reabsorption?

Excess water, mineral salts, nitrogeneous waste products, uric acid and creatine pass out of collecting duct into reval pelvis -- urine

Kidney failure common causes

high blood pressure, diabetis, alchohol abuse, accidents damaging kidney, complications during surgery

How to deal with failed kidney

Kidney transplant (requires suitable donor), haemodialysis (device to stimulate excretion mechanism of kidneys) and peritoneal dialysis

What happens during haemodialysis

Blood is chanelled from the vein into the dialyser of a dialysis machine
Blood flows into the tubing of the dialyser. Tubing is bathed in controlled dialysis fluid
Walls of tubing is partially permeable

Small molecules like urea and other metabolic waste products diffuse out of tubing into dialysis fluid

Bloocells and platelets and large molcules remain

Features of dialysis machine