Human Endocrine System Flashcards
Homeostasis
What is Homeostasis
Homeostasis is the tendency of living organisms to maintain a constant composition of their internal environment within narrow limits irrespective of changes in the external environment. The internal environment of multicellular organisms is the tissue fluids in which the cells are bathed.
Maintaining oxygen and carbon dioxide levels
As a result of increased physical activity the rate of cellular respiration increases to release more energy.
Increased cellular respiration also releases more carbon dioxide that gets into the blood.
The increased carbon dioxide causes the medulla oblongata of the brain to become stimulated.
The medulla oblongata sends impulses to the heart and to the breathing muscles.
The heart beats faster and blood carrying carbon dioxide is pumped faster to the lungs from the tissues.
The breathing muscles (the diaphragm and intercostal muscles) cause the breathing movements (inhalation and exhalation) to be speeded up. The abdominal muscles also help to push up the diaphragm with greater force.
Carbon dioxide is removed out of the body more quickly and more oxygen is taken in rapidly and supplied to the tissues.
In this way, the levels of oxygen and carbon dioxide are brought back to their normal limits.
Maintaining water levels
The nephron controls the amount of water in the blood. It is responsible for osmoregulation. When the body has too much water, the nephron extracts the water from the blood and passes it to the bladder. When the body looses too much water, the nephron reacts to retain as much water as possible.
When the body has too much water
Due to low temperature, inactivity or the intake of a large amount of fluids.
The volume of water in the blood increases
Osmoreceptors in the hypothalamus are stimulated.
and a message is sent to the pituitary gland which secretes less ADH into the blood.
Because of reduced levels of ADH the walls of the distal convoluted tubule and collecting tubule become less permeable.
This causes less water to leave the tubule by osmosis and enter the medulla oblongata.
More water thus remains in the tubule forming very dilute urine which is excreted from the body.
Less water is thus reabsorbed into the capillaries
In this way the level of water in the blood decreases.
When the body has too little water
Due too high temperature, strenuous activity or insufficient intake of fluids, the volume of water in the blood decreases.
Osmoreceptors in the hypothalamus are stimulated
and a message is sent to the pituitary gland which secretes more ADH into the blood.
Because of increased levels of ADH, the walls of the distal convoluted tubule and collecting tubule become more permeable.
This causes more water to leave the tubule and enter the medulla.
The water that is in the medulla is re-absorbed at a faster rate by the blood capillaries
The amount of water in the blood thus increases
The tubule however has less water, forming concentrated urine which is excreted from the body.
Maintaining Salt Levels
The amounts of sodium ions is excreted can be regulated as follows:
When there is a shortage of sodium in the blood
The adrenal gland secretes more aldosterone
More sodium is thus reabsorbed by the blood capillaries of the distal and collecting tubules.
So that less sodium ions are thus excreted.
In this way the amount of sodium increases back to normal.
When there is an excess of sodium in the blood
The secretions of aldosterone from the adrenal gland decreases.
Less sodium is thus reabsorbed by the blood capillaries
allowing more sodium to be excreted
The amount of sodium in the blood decreases back to normal.
Temperature Regulation (Thermoregulation)
The organ responsible for thermoregulation in humans is the skin.
Structure of the human skin
The skin is made up of an outer, epidermis and an inner dermis.
The epidermis in turn is made up of 4 layers: viz: Horny layer - flattened and dead cells in which the protein keratin is deposited., Non-glandular (clear) layer, Glandular layer, Germinative layer- actively dividing cuboidal cells, replaces cells lost from horny layer, pigment within cells gives the skin its colour.
The dermis is made up of dense connective tissue and contains the following:
Blood and lymph vessels
Nervous and sense receptors
Sebaceous glands
Sweat glands and sweat ducts
Hair follicles
Erector muscles
Adaptions of the Human Skin for Thermoregulation
The parts of the skin that contains greatly to the regulation of the body temperature are the sense receptors, the hair on the skin, the blood vessels and the sweat glands.
Sense receptors
Various types of receptors that convert stimuli to impulses and transmit these by nerves to the Central Nervous System.
Blood Vessels in the Skin
Contains smooth muscles that allow it to dilate to send more blood to skin to encourage heat loss. They may also constrict to reduce blood flow to the skin to decrease heat loss to the environment.
Sweat Glands
Connected to a sweat pore to allow sweat to come to lie on the surface of the skin from where it evaporates. Sweat glands may become more active to increase sweat loss thus allowing for greater heat loss. May also become less active, reducing sweat production and therefore heat loss.
