Homeostasis

Question 1

Define

Homeostasis

Answer 1

Homeostasis is the maintanance of a relatively constant internal environment

Question 2

How is homeostasis achieved?

Answer 2

1. Stimulus: A change in environment
2. Receptor: Sense organ or structure that detects the stimulus
3. Self reglulating corrective mechanism: Internal processes that take place in opposition to the stimulus
4. Negative feedback: As corrective mechanism takes place, the stimulus gradually decreases in intensity, correspondingly decreasing the intensity of the corrective mechanism

Question 3

How is blood glucose concentration regulated in the human body?

Answer 3

1. Blood glucose conc. increases/decreases below norm
2. Detected by receptor, Islets of Langerhans in pancreas
3. Islets of Langerhans secretes more insulin/glucagon
4. Permeability of cell membranes to glucose increases/decreases
5. Liver cells convert excess glucose to glycogen/glycogen to glucose
6. Concentration of blood glucose decreases/increases
7. Sends negative feedback to receptor
8. Decreases in intensity as concentration returns to normal

Question 4

What are high GI and low GI foods?

Answer 4

High glycaemic index foods (>70): Carbs break down quickly
Low glycaemic foods (<55): Carbs break down slowly

Question 5

Functions of the skin

3 functions

Answer 5

1. Protection; against mechanical impacts and pressure, microorganisms, radiation and toxic chemicals
2. Regulation; regulates aspects of internal environment, including body temperatures
3. Sensation; receptors for heat, cold, touch and pain

Question 6

Describe the strucures of the skin

Answer 6

1. Three layers: Epidermis, dermis, hypodermis/subcutaneous layer
2. Thermoreceptors: Nerve endings that pick up changes in temperature
3. Skin capiliares: Capiliaries that let blood flow close to the skin surface
4. Arterioles: Muscle walled vessels found in the dermis
5. Sweat glands: Secrete sweat that travels through sweat ducts to sweat pores on skin
6. Sebaceous glands: Secrete sebum that prevents bacteria from settling on skin. Prevents dehydration of skin by ‘locking in’ moisture levels
7. Hair erector muscles: Able flatten or raise hair shaft by relaxing and contracting
8. Adipose cells: Found in hypodermis. Conservation of heat as fats are good insulators of heat

Question 7

Explain the role of blood vessels in thermoregulation

Answer 7

1. Arterioles: Carry blood from artery towards shunt vessels and capiliaries. Able to constrict and dilate to control amount of blood flowing to skin capiliaries
2. Shunt vessel: Directly connects arteriole to venule to bypass skin capiliaries
3. Capiliaries: Connects arterioles to venules, found near the skin surface hence heat dissipates easily.

In a warm environments, arterioles dilate and shunt vessels constrict, hence more blood flow to the capiliaries near the skin surface. Hence more heat is lost by conduction, convection and radiation.

Vice versa for cold environments

Question 8

Role of hair in thermoregulation

Answer 8

In a cold environment, hair erector muscles contract, causing hair to become more upright, trapping an insulating layer of air around the skin, minimising heat loss as air is a poor conductor of heat

In a hot environment, hair erector muscles relax, causing hair to lay flat on the skin. Air circulates over the skin, removing heat

Question 9

How is heat regulated in the human body?

Answer 9

1. Stimulus: Blood and skin temperature increase/decrease
2. Receptor: Thermoreceptors on skin detect change, hypothalamus monitors blood temperature
3. Corrective mechanism: Vasodilation/vasoconstriction of skin arteries, more/less blood flow to capiliaries, increasing/decreasing heat loss to surroundings; sweat glands more/less active increasing/decreasing heat loss by latent heat of vapourisation; increased rate of breathing, metabolic rate decrease (hot), shivering, meatabolic rate increases (cold)
4. Body temperature returns to normal, providing the negative feedback for intensity of corrective mechanism to decrease