A2 Unit 3.7 Homeostasis and the kidney

What is Homeostasis, The 3 Homeostatic Control Systems & it’s importance?

The maintenance of a state of dynamic equilibrium (constant environment) within a living organism despite fluctuations in internal and external conditions, by negative feedback.

Homeostatic Control Systems:

1. Blood glucose levels

2. Thermoregulation

3. Osmoregulation

Homeostasis is important to ensure optimum conditions for enzymes and cellular processes in the body.

What is Negative & Positive Feedback?

Negative Feedback - Self-regulatory mechanisms return the internal environment to the optimum (set point) when there is a fluctuation.

Positive Feedback - A fluctuation which triggers changes that result in an even greater deviation from the normal level.

The set point is a desired value or range of values determined by a coordinator.

How does negative feedback work?

• A receptor is a specialised cell located in sense organs that detect a specific stimulus/ a deviation from the set point in the internal environment.

• The receptor sends instructions to a co-ordinator or controller.

• The coordinator coordinates information from the receptors and sends instructions to the effectors, which make responses which are corrective.

• Effectors are muscles or glands which enable a physical response to a stimulus.

• The factor returns to normal (the set point), this is monitored by the receptor and information is fed back to the effectors, which stop making the correction.

Excretion

Urea - Excess amino acids are deaminated in the liver; the amino group is removed and converted into ammonia (highly toxic) and then to urea (less toxic). Urea is removed by the kidneys.

The Kidney & Labelled Diagram

The kidney has two main functions:

1. Excretion – the removal of nitrogenous metabolic waste from the body

2. Osmoregulation – the mechanism by which the balance of water and dissolved solutes is regulated (control of water potential of the body’s fluids)

• Medulla (reabsorption of water occurs here)

• Cortex (ultrafiltration and selective reabsorption occurs in this region)

• Renal Pelvis (empties urine into the ureter)

• Ureter (transports urine to the bladder)

Kidney Structure

Humans have two kidneys, one either side of the vertebral column. The kidney is enclosed in a tough renal capsule. Blood enter the kidney via the renal artery and leaves the kidney via the renal vein.

The Nephron

The nephron is the functional unit of the kidney and is highly adapted. There are a million nephrons in every kidney.

Bowman’s capsule and the proximal and distal convoluted tubules are present in the cortex.

The loop of Henle is found in the medulla.

Ultrafiltration