homeostasis and hormonal control (chap 9) -olevel pure bio

what is homeostasis

what is homeostasis

the maintenance of a constant internal environment, helping an organism be independent from changes in the external environment

what is the negative feedback process

when the body reacts to bring about an opposite effect to the changes detected

what must there be for the negative feedback process to occur

• a normal or set point that needs to be maintained

• a stimulus which is a change from normal condition in the internal environment

• receptors that detect the stimulus

• a corrective mechanism that brings about reverse effects of the stimulus

what is a hormone

• a chemical substance produced in minute quantities by an endocrine gland

• transported by the bloodstream to a target organ

• influence growth, development and activity of an organism

• destroyed in the liver and excreted by kidneys after performing their functions

what are endocrine glands

• ductless glands that transport their secretions through the bloodstream

• eg: pituairy gland, pancreas (islet of Langerhans which secrete the hormones insulin and glucagon into the bloodstream)

what are exocrine glands

• ducts present to transport secretions to target organs

• eg: sweat gland, salivary gland, pancreas (pancreatic juice carried by the pancreatic duct to the duodenum)

describe the pituitary gland

• referred to as the ‘master gland’

• secretes many hormones which control the secretion of hormones of other endocrine glands

• secretes ADH (antidiuretic hormone)

describe the hypothalamus

• endocrine gland that regulates the secretion of some hormones

what happens when blood glucose rises above normal

• stimulus: blood glucose rises above normal

• receptor: islet of Langerhans detects stimulus

• corrective mechanism: islet of Langerhans secrete more insulin into bloodstream. blood transport insulin to liver and muscles causing

  • increase in the rate of glucose uptake by cells

  • making cell membranes more permeable to glucose - glucose is absorbed more quickly by cells

  • insulin increases rate of respiration

  • insulin causes the liver and muscles to convert excess glucose to glycogen. glycogen is stored in liver and muscles

• blood glucose concentration decreases and insulin production is reduced

what happens when blood glucose concentration drops below normal

• stimulus: blood glucose drops

• receptor: islet of langerhans detect stimulus

• corrective mechanism: islet of langerhans secrete more glucagon into the bloodstream. blood transport the glucagon to the liver and muscles

  • glucagon converts glycogen to glucose

  • converts fats and amino acids to glucose

symptoms of diabetes

• consistently high blood glucose concentration

• presence of glucose in urine after a meal

• healing of wounds is slow and difficult

• frequent urination

• weightloss

what happens when body temperature increases

1. thermoreceptors in the skin detect rise in external temperature and send nerve impulses to the hypothalamus

2. arterioles in the skin dilate/ undergo vasodilation to allow more blood to flow through blood capillaries in the skin so more heat from the blood will be lost through the skin

   sweat glands become more active and produce more sweat. when water in the sweat evaporates from the surface of the skin, more heat is lost from the body

   metabolic rate is decreased to reduce heat released in the body

3. after a increase in heat loss and a decrease in heat production, body temperature decreases back to normal

what happens when body temperature decreases

1. thermoreceptors in the skin are stimulated and send nerve impulses to the hypothalamus. the hypothalamus sends nerve impulses to relevant parts of the body to bring about changes in the body.

2. arterioles in the skin constrict (vasoconstriction). less blood flows through blood capillaries in the skin. hence, less heat will be lost through the skin.

   sweat glands become less active and produce less sweat so less water evaporates from the surface of the skin, and less heat is lost from the body

   metabolic rate increases to increases the amount of heat released within the body.

   when above processes are not enough to prevent drop in body temperature, shivering occurs. the rapid contraction and relaxation of skeletal muscles increase amount of heat released

3. after a decrease in heat loss and increased heat production, body temperature increases back to normal

what happens when water potential in blood increases above normal

receptor: hypothalamus detects stimulus

corrective mechanism:

• less antidiuretic hormone is released by pituitary gland into the bloodstream

• less antidiuretic hormone is transported to the kidneys

• cells in the walls of the collecting ducts become less permeable to water

• less water is reabsorbed into the bloodstream

• more water is excreted and urine is more diluted

water potential decreases back to the normal level

what happens when water potential decreases below the normal level

receptor: hypothalamus detects stimulus

corrective mechanism:

• more antidiuretic hormone is released by pituary gland into the bloodstream

• more antidiuretic hormone is transported to the kidneys

• cells in the walls of the collecting ducts become more permeable to water

• more water is reabsorbed into the bloodstream

• less water is excreted and urine is more concentrated

water potential increases back to normal level