Biology 3.7 - homeostasis and the kidney

What is homeostasis?

The mechanism by which a constant internal environment is achieved within a living organism

Why is regulation of an internal environment vital?

• maintains optimal conditions for cell function

• protects cells from changes in the environment

What are some factors that are kept constant in mammals?

• Core body temperature

• Blood glucose concentration

• Solute potential of blood

• blood pH

How do the factors such as body temperature change?

• They fluctuate due to body activity or environmental conditions

• homeostasis prevents wild fluctuations

• fluctuations are small and about a set point

The body is kept in a dynamic equilibrium, what does this mean?

Constant changes occur but corrective mechanisms bring the internal environment back towards the set point

What are the stages involved in a negative feedback system?

1. A set point or norm at which a system operates (determined by a control centre/co-ordinator)

2. A receptor/detector - detects and monitors the level of a factor and its deviation from the set point and sends instructions to…

3. A control centre/co-ordinator - evaluates the information and communicates with one or more effectors (muscles, glands)

4. An effector - carries out a corrective response + factor returns to the set point

Explain negative feedback system that controls glucose concentration in the plasma

• increase above normal

• detected by pancreas

• pancreas releases insulin into the bloodstream

• to target cells (liver + muscle)

• take up more glucose from blood + convert it to glycogen

• decrease in blood glucose

• decrease below normal

• detected by pancreas

• pancreas releases glucagon into bloodstream

• target liver cells

• breakdown of glycogen into glucose

• glucose moves into blood

• increase in blood glucose

What is positive feedback?

When an effector increases a change i.e., movement away from the norm causes a further movement away from the norm

Example of positive feedback

Oxytocin

• stimulates contraction of the uterus at the end of a pregnancy

• contractions stimulate production of more oxytocin

• increases the stimulus i.e. more uterine contractions

What is excretion?

the removal of waste products of metabolism from the body

What are the 4 excretory organs?

• lungs

• kidneys

• skin

• liver

Lungs…

excrete water vapour and CO₂

in air

through respiration

Kidneys…

excrete urea, uric acid and creatine

in urine

through amino acid breakdown, nucleic acid breakdown, and muscle tissue breakdown

Skin…

excrete urea

in skin

through amino acid breakdown

Liver…

excrete bile pigments

in faeces

through haemoglobin breakdown

How is water removed from the body?

• tears

• sweat

• breathing out/water vapour

• urination

• faeces

• saliva

• mucus

What are the 2 functions of the kidney?

1. excretion

2. osmoregulation

What is excretion?

The removal waste products of metabolism e.g. urea

• kidneys filter the blood and remove waste as urine

What is deamination?

• Removal of amine group from excess amino acids

• amine group converted to urea

• urea is transported to kidney and filtered out of blood

What is osmoregulation?

the control of water content and solute composition of body fluids such as the blood, tissue fluid and lymph

urinary system

LS of kidney

single nephron