A2 1 - Homeostasis

CCEA A2 1 Biology Homeostasis and the Kidney

What are the two forms of coordination in multicellular animals?

What are the two forms of coordination in multicellular animals?

1. Nervous - rapid response between specific parts

2. Endocrine - Slower and less specific

What is Homeostasis?

The maintenance of constant or steady state conditions within the body.

What are the stages of a self-regulating system?

• Set point - the desired level at which the system operates moderated by receptors

• Receptors - this detects any deviation from the set point and informs the controller

• Controller - coordinates information from various sources and sends instructions to an appropriate effector

• Effector - that brings about the necessary change needed to return the system to the set point. This returns normally creates a feedback loop.

• Feedback loop - informs the receptor of the changes to the system brought about by the effector

What occurs when there’s a deviation from the set point that causes changes that result in an even greater deviation from the normal?

Positive Feedback

Why is homeostasis important?

• Enzymes - control biochemical reactions within the cells and proteins are sensitive to temperature and pH

• Water potential - changes to this in blood and tissue fluid may cause cells to shrink or expand, and then the cells will not operate normally

• Biochemical reactions are in dynamic equilibrium- changes can alter the equilibrium

• Maintain a constant internal environment independent of external - they will have a wider geographical range and therefore have a greater chance of finding food and shelter

What environmental features affect the functioning of the cell?

1. Temperature - Too low=slow reactions Too high=denature protein

2. Amount of Water - Lack=reaction slow/stop Too much=cells swell/burst

3. Amount of glucose - Too little=reduced respiration Too much=water drawn out

What is excretion?

The removal of toxic waste from metabolism e.g. Urea/Nitrogenous gas/ammonia, CO2 and bile to prevent them from becoming toxic

The Kidney

An organ which removes toxic waste products of metabolism and maintains the optimal water potential of body fluids.

What the two functions of the kidney?

1. Excretion - producing urine

2. Osmoregulation - controlling water balance in body

How does the Kidney work?

Ultrafiltration followed by selective reabsorption.

What do the Kidneys consist of?

Millions of nephrons

what is each kidney surrounded by?

a layer of adipose (fat) tissue and a layer of connective tissue.

How do the layers of tissue surrounding the kidney serve it?

Keep the kidneys in position and protect them from mechanical damage.

Fibrous Capsule

An outer membrane that protects the kidney

Cortex

A lighter coloured outer region made up of bowman’s capsules, convoluted tubules and blood vessels

Medulla

A darker region made up of loops of Henle, collecting ducts and blood vessels

Renal Pelvis

A funnel shaped cavity that collects urine into the ureter

Renal Artery

A funnel shaped cavity that collects urine into the ureter

Renal artery

Supplies the kidneys with blood from the heart via tha aorta

Renal vein

Returns blood to heart via vena cava

What’s the functional unit of the kidney?

Nephron

Hoe long is a nephron?

14mm

What is each nephron made up from/originates as?

Bowman’s Capsule which is cup-shaped.

what does the bowman’s capsule contain/made up of?

Supplied with blood from the afferent arteriole A mass of blood capillaries known as the glomerulus. Its inner layer is made up of specialised cells called podocytes.

Whats the proximal convoluted tubule?

a series of loops surrounded by blood capillaries. Its walls are made up of cuboidal epithelial cells with microville.

Whats the loop of Henle?

A long hairpin loop that extends from the cortex into the medulla of the kidney and back again. Blood capillaries surround it.

Whats the distal convoluted tubule?

A series of loops surrounded by blood capillaries. Its walls aew made from cuboidal epithelial cells but it is surrounded by fewer capillaries than the proximal tubule.

Whats the collecting duct?

A tube into which a number of distal convoluted tubules empty. It is lined by cuboidal epithelial cells and becomes increasingly wide as it empties into the renal pelvis. Bundles of collecting ducts form pyramids.

Whats the afferent arteriole?

A tiny vessel that ultimately arises from the renal artery and supplies the nephron with blood. The afferent arteriole enters the renal capsule of the nephron where it forms the glomerulus.

Whats the glomerulus?

A many branched tuft of capillaries from which fluid is forced out of the blood. The glomerular capillaries recombine to form the efferent arteriole.

Whats the efferent arteriole?

A tiny vessel that leaves the renal capsule. It has a smaller diameter than the afferent arteriole and so causes an increase in hydrostatic pressure within the glomerulus. The efferent arteriole carries blood away from the renal capsule and later branches from the peritubular capillaries.

Whats the peritubular capillaries?

a concentrated network of capillaries that surrounds the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule and from where they reabsorb mineral salts, glucose and water. The peritubular capillaries merge together into venules that in turn merge together to form the renal vein.

What is Ultrafiltration?

The filtration of plasma and substances below a certain size into the bowman’s capsule due to high hydrostatic pressure and the presence of small molecules.

How many layers are in the bowmans capsule/renal capsule?

three layers

What is the first layer of the bowman’s capsule?

Capillary endothelium - squamous endothelium of the capillary which in the glomerulus this single layer of cells has thousands of pores.

Whats the second layer of the bowman’s capsule?

The basement membrane between the two layers composed of glycoproteins and collagen fibres - extracellular matrix. Mesh like structure acts as the filter.

Whats the third layer of the renal capsule?

Podocytes which are lifted off the surface on little ‘feet’ and so allows the filtrate to pass beneath them and through the gaps in their branches.

How does the basement membrane act as an effective filter?

Stops large molecules from getting through. As a result red blood cells, white blood cells and plasma proteins can’t pass across. Other substances up to a relative molecular mass are squeezed out of the capillary into the filtrate, e.g. glucose, amino acids, salts, water, urea.