EXCRETORY

SYSTEM

EXCRETION IS IMPORTANT FOR HOMEOSTASIS

EXCRETION:

Is the name given to the removal from the body of:a) waste products of its chemical reactionsb) The excess of water and salts taken in with the diet c) Spent hormonesd) Drugs and foreign substances

Production and release of USEFUL substances in the body

(saliva/hormones)

SECRETION:

WATER

INTRACELLULAR : inside the cells

(30 litres)INTERCELLULAR: tissue fluid

(9litres)

PLASMA (3 litres)

EXCRETION

Metabolic processes in cells may produce toxic compounds. The two most significant are:

1) Carbon dioxide: which dissolves to form a weakly acidic solution in blood and tissue fluid

2) UreaBoth of them can denature enzymes.

Excretory organs:Lungs: they supply the body with O2but

they also get rid of CO2.

Kidneys: the kidneys remove urea and nitrogenous waste from the blood. They also expel excess of water, salts, hormones and drugs. (expelled with the faeces)

Liver: it excretes bile pigments, bilirubin. Bilirubin, the breakdown product of haemoglobin, is secreted into the small intestine and it gives the colour to the faeces

Skin: the skin loses incidental water, salts and urea when you sweat. However, sweating is a response to a rise in temperature and not to a change in blood composition.

How urea is made

Excretory System

The kidneys are two fairly solid, oval structures.

They are located on each side of the spine.

They are red brown, enclosed in a transparent membrane attached to the back of the abdominal cavity.

KIDNEYS

Renal artery: branches off from the aorta and brings oxygenated blood to the kidneys.

Renal vein: takes deoxygenated blood away from the kidneys to the vena cava.

Ureter: is a tube which runs from each kidney to the bladder in the lower part of the abdomen.

Urethra: is a tube that connects the urinary bladder to the genitals for removal out of the body.

Urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. Urine enters the bladder via the ureters and exits via the urethra.

The external urethral sphincter is a striated muscle that allows voluntary control over urination.

A kidney cut by its length:

CORTEX: it is the dark outer region.

MEDULLA: lighter inner zone

PELVIS: where the ureter joins the kidney

CORTEX: It contains the bowman’s capsules in which the ultra filtration of blood takes place.

MEDULLA: it contains loops of Henle and collecting ducts.

NEPHRON Nephron is the basic

structural and functional unit of the kidney.

There are up to 4 million nephrons in a kidney.

It’s a single glomerulus with its renal capsule, renal tubule and blood capillaries.

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Its main function is to 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.

A nephron eliminates wastes from the body, regulates blood volume and blood pressure, controls levels of electrolytes and metabolites, and regulates blood ph.

Branch of renal artery

First coiled tubuleBowman

capsule

Collecting duct

urine

NEPHRON:

Loop of Henle

Kidneys tubules: Branch of renal artery: (WIDE): blood with high

urea concentration is delivered to the kidneys and gets to the GLOMERULUS (NARROW)

Renal capsule: filtration of blood under high pressure to remove toxic urea. Unfortunately useful glucose, amino acid, salts and water also leave the blood. RED CELLS/PROTEINS/LIPIDS stay

First coiled tubule: here the useful solutes, glucose, amino acids and some minerals are selectively reabsorbed into the blood. (process of absorbing back the substances needed by the body) Up to 90% of water is reabsorbed here.

Collecting duct: kidney can reabsorb water from here and return it to the blood according to the body’s demands.

Remember: urea is produced in the liver but excreted by the kidneys.

Revise how urea is made by liver cells by un excess of amino acids.

Urine: mainly water with concentrated urea and excess salts.

So…The nitrogenous waste products, excess

salts and water continue down the renal tubule into the pelvis of the kidney. From here the fluid, now called urine, passes down the ureter to the bladder.

How toxic waste from cellular respiration (catabolism) is excreted

1- Blood + waste come to kidneys by renal artery.

2-Filtration of waste in the nephron.

3-Reabsorption of some useful products that could have been filtered, to the capillaries surrounding the nephron.

4-Waste is concentrating as urine.

5-Urine goes to the -collecting duct - ureter - bladder - and goes out by urethra

holds 300-350 ml of urine.

• As urine accumulates, the wall of the bladder thins as it stretches, store larger amounts of urine without a significant rise in internal pressure.

When the bladder reaches around 25% of its working volume urge to urinate starts (Easy to resist)

Eventually, the bladder will fill to the point where the urge to urinate becomes overwhelming

How can our body keep the percentage of water in our body around 60/70%?

60 – 70 % of the weight of our body is water (around 40 l of water).

If it is very hot and we sweat, we lose some of our body water composition.

If we lose water, we can suffer dangerous dehydration

We have to” save” water and we must not lose more water through urine.

The urine will be more concentrated (water is reabsorbed)

If we drink a lot of water, we have an extra supply of water (that we don’t need).

Our urine will be more diluted (water will not be reabsorbed in kidneys).

Water balance and Osmoregulation

we gain water food/drink we lose water by *evaporation (skin/lungs)

* urination* defecation

*Keep the concentration of the body fluids

*adjust the concentration of BLOOD too dilute water is absorbed

too concentrated water is absorbed

Stimulates HYPOTHALAMUS (a “THIRST” centre in the brain )

stimulates PITUITARY GLAND secretes ADH blood

Blood kidneys kidney tubule absorb MORE water +concentrated urine

Negative feedback happens when the response to a given action generates an effect that inhibits that action.

In a variety of processes: blood pressure control, glycemic control, muscle contraction,

TISSUE FLUID

If it is TOO CONCENTRATED, it will withdraw (=extraer) water from the cells (by OSMOSIS) and the body

dehydrates

Supplies or removes the substances to or from the cells

If it is TOO DILUTE cells will take up too much water (by OSMOSIS) and the tissues become swollen

Composition of the TISSUE FLUID (its concentration, acidity and temperature) in the body is adjusted all the time to keep it STEADY

What is HOMEOSTASIS, Sheldon?

Organs that contribute to Homeostasis

KIDNEYS•Remove substances that might poison the enzymes•Control the level of SALTS, WATER, ACIDS (ures/uric acid) in the blood

LIVER •Regulates the level of GLUCOSE (it affects the brain cells) and amino acids

Lungs

•Keep the concentration of Oxygen and Carbon dioxide in the blood for the cell’s reactions (respiration)

Control by the

Dialysis Machine

Kidney failure can be the result of *A drop in blood pressure (recovery is

spontaneous/more than 2 weeks leads to failure)

*Disease of the kidneys with 1 kidney

we can survive/ if both kidneys fail Dialysis machine

It consists of a cellulose tube coiled up in a water bath

* is kept at body temperature and it is constantly changed as unwanted blood solutes accumulate in it.

* is a solution of salts and sugar of the correct composition only substances above this concentration (UREA, URIC ACID, EXCESS SALTS) are removed

Submicroscopic pores in the dyalisis tubing allow small molecules to leak out into the water bath (= FILTRATION process in the glomerulus)

Has to spend 2/3 nights a week in the diayalisis machine

Water bath

KIDNEY TRANSPLANT

Better solution

2 problems: a. to find donors (a close relative/healthy person who dies in an accident) b. REJECTION body produces Lymphocytes which attack and destroy the new organ

Overcome by•Choosing tissues similar to the patient’s•Using immunosuppressive drugs

Some IGCSE questions

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