Chapter 5 - homeostasis (blood glucose and body temperature)

homeostasis

the maintenance of a constant internal environment despite changes in the external environment

homeostasis maintains:

• temperature

• hormones

• blood glucose

• water

• gas

• pH

how is homeostasis dynamic?

during homeostasis the conditions of the body fluctuate (increase and decrease), this means the conditions are constantly changing to keep them optimal

fluctuation called a dynamic equilibrium

components of homeostasis?

• stimulus

• receptor

• modulator/ control centre

• effector

• response

stimulus

the change in the environment

receptor

the component detecting the change (can be external or internal)

modulator/ control centre

processes the information - usually medulla or hypothalamus

effector

carries out the counteractive response - always muscles or glands

response

identifiable change

negative vs positive feedback loop

in a negative feedback loop the response means the response changes in the OPPOSITE direction to the original stimulus e.g. thermoregulation

whereas

in a positive feedback loop the response means the response changes in the SAME way to the original stimulus e.g. contractions

what are the two types of responses to homeostasis?

physiological (unconscious) e.g. sweating

behavioural (conscious) e.g. putting on a fan

set point

the ideal conditions that the body fluctuates around in homeostasis

tolerance limits

the lower and upper limits of the fluctuation

normal glucose levels in the body

4-6mmol/L or 90mg/100mLg

glycogen

glucose is converted to glycogen when levels in blood are high - glycogenesis

converted back to glucose when blood levels drop

glycogen is stored in liver and muscle cells

large, storage molecule

livers role in regulation of blood sugar

carbohydrates are broken down in the small intestine to glucose, then absorbed into the blood capillaries

moves to liver via hepatic portal vein

liver can:
remove glucose from blood to be used for energy for liver cells

convert it to glycogen

if liver has enough glucose, can allow to circulate around body

excess glucose and glycogen can be further converted into fat (adipose tissue) for long term storage

glycogenesis

formation of glycogen from glucose

stimulated by insulin release from beta cells

glycogenolysis

breaking down of glycogen

converted back to glucose when it is required by the liver or muscle cells

stimulated by glucagon release from the alpha cells in the pancreas

role of the pancreas in controlling blood glucose levels

hormones are secreted from cells in the pancreas called the islets of Langerhans

two types of islets of Langerhans cells

alpha cells = release glucagon, which increases blood sugar by glycogenolysis, releasing glucose from glycogen

beta cells = release insulin, which decreases the blood sugar by glycogenesis, which creates glycogen from glucose

role of the adrenal cortex in maintenance of blood sugar

secretes glucocorticoids such as cortisol

these increase metabolism in higher stress levels - under direction of ACTH from the anterior pituitary

stimulate conversion for glycogen into glucose

increases amino acid removal from cells

promotes mobilisation of fatty acids into adipose tissue

gluconeogenesis

the stimulation of the liver to produce glucose from fats and amino acids

lipogenesis

the conversion of glucose into fats

lipolysis

breakdown of lipids into glucose

role of adrenal medulla in blood sugar levels

secretes adrenaline and noradrenaline

similar effects as the sympathetic nervous system

counteracts insulin effects

stimulates production of glucose via conversion of glycogen

negative feedback loop for increased blood glucose levels

STIMULUS = increased blood glucose levels

RECEPTOR =chemoreceptors in islets of langerhans in the pancreas

MODULATOR = beta cells within islets of langerhans of pancreas secretes insulin

EFFECTOR = liver and skeletal muscle respond to the insulin

RESPONSE = glycogenesis - glucose into glycogen, body cells have an uptake of glycogen, lipogenesis into long term glucose storage in fat.

FEEDBACK = lowered blood glucose levels

negative feedback loop for low blood glucose levels

STIMULUS = lower blood glucose levels

RECEPTOR = chemoreceptors on the islets of langerhans in the pancreas

MODULATOR = alpha cells in islets of langerhans in the pancreas secretes glucagon in the blood

EFFECTOR = liver and skeletal muscle

RESPONSE = glycogenolysis, gluconeogenesis, lipolysis, all release glucose

FEEDBACK = negative, higher blood glucose levels

normal temperature in the body

37 degrees Celsius

radiation

no direct contact with source

e.g. from sun or fire

can result in gain or loss

convection

when hot or cold air passes over the body

e.g. fan or a heater

can result in gain or loss

conduction

direct contact with heat source

e.g. standing on hot sand with bare feet

can result in gain or loss

evaporation

transformation of water from its liquid state to its gas

e.g. steaming

heat loss only

heat production in thermoregulation

glucose is broken down in the process of respiration - energy is released producing heat as a byproduct

metabolic rate = the rate at which energy is released by the breakdown of food

heat detection in thermoregulation

thermoreceptors = peripheral thermoreceptors found in skin or mucous membranes to detect changes in the environment

two types:
heat: detect higher environmental temp
cold: detect lower environmental temp

central thermoreceptors are located in the hypothalamus to monitor core body temp

role of the skin in thermoregulation

sweating, changing diameter of blood vessels

heat lost by conduction, convection, radiation and evaporation

prevention of falling body temp

vaso-constriction of blood vessels (smooth muscles) in the skin so that less heat can be transferred

piloerection = hair standing up

increased metabolic rate through: stimulation of adrenal medulla and release of adrenaline and noradrenaline

shivering = hypothalamus sends impulses to skeletal system to increase muscle tone —> muscle tremors

behavioural = curl up, put on more clothing

prevention of rising body temp

vasodilation of blood vessels near the skin so that less heat can be transferred

decrease of metabolic rate through a reduction in thyroxine production from the thyroxine gland

sweating = produces cooling effect by evaporation

behavioural = turn on the AC, less clothing