homeostasis
define homeostasis and its importance
homeostasis is the maintenance of a constant internal environment within tolerable limits. it is to achieve a certain degree of independence from the external environment, so that the internal environment is maintained in optimal condition and in a state of maximum efficiency. it is also important for optimal functioning of physiological processes as well as component cells, tissues, organs, and organ systems.
define endocrine system
a collection of endocrine glands that secrete hormones directly into the bloodstream to be carried towards target cells/organs
define excretion and its importance
excretion is the removal of toxic materials and metabolic waste products from an organism. metabolic waste products, if allowed to accumulate, can be harmful and prevent the maintenance of a steady state in the body.
describe the function and adaptations of red blood cells
RBCs transport oxygen and carbon dioxide to body cells
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1. biconcave shape
- increase surface area to volume ratio
- increase rate of diffusion of oxygen and carbon dioxide
2. presence of haemoglobin
- haemoglobin combines reversibly with oxygen to form oxyhaemoglobin
- enables RBCs to transport oxygen from lungs to other body cells
3. absence of nucleus
- allows more haemoglobin to be packed into an RBC
4. elastic, can be bell-shaped
- RBCs can squeeze through blood cells smaller than itself in diameter without breaking
define negative feedback mechanism
a coordination of response(s) to a stimulus by the nervous and endocrine system
criteria for homeostasis (6)
1. norm to be maintained
2. stimulus (aka change from normal conditions)
3. receptor to detect stimulus and send signal to control centre
4. control centre (to coordinate info from receptors and send out instructions to correct the deviation)
5. corrective mechanism (bring about reverse effect of stimulus)
6. negative feedback sent to control centre via receptor (stops corrective mechanism when norm is reached)
describe the secretion of adrenaline
1. stimulus is detected by hypothalamus in the brain
2. impulses are transmitted down the spinal cord
3. the motor neurone transmits impulses to the adrenal gland (above kidneys)
4. adrenal gland secretes adrenaline into the bloodstream
5. blood transports adrenaline to the target organs
name the parts of the human urinary system and their functions in excretion
1. kidneys
- contain numerous kidney tubules which remove urea, excess water, and heat from the blood to form urine
- responsible for osmoregulation
2. ureter
- a tube connecting the kidney to the bladder through which urine flows from the kidneys to the bladder
3. bladder
- a muscular bag that stores urine
4. urethra
- a muscular tube through which urine flows from the bladder to the exterior
describe the process of blood clotting
1. when blood vessels are damaged, damaged tissue and platelets produce thrombokinase (enzyme)
2. thrombokinase converts prothrombin into thrombin (enzyme)
3. thrombin converts soluble fibrinogen into insoluble fibrin threads that trap blood cells
4. the whole mass forms a scab/clot
- undamaged blood vessels contain an anti-clotting substance aka heparin
- when thrombokinase in released in damaged tissues, it neutralises heparin so clotting can occur
describe what would happen if the wrong blood type were transfused
- incompatible transfusions can lead to agglutination aka binding of antibodies in recipient's plasma to antigens on donated RBCs
- RBCs become cross-linked to one another and trigger immune system to rupture RBCs, released haemoglobin may cause liver damage
- agglutination can lead to death as clumps may block up small vessels and prevent blood flow
principles of homeostasis (4)
1. in homeostatic control, the body reacts to bring about an opposite effect to the stimulus detected
2. disturbance sets a sequence of events in motion, aka corrective actions, to restore the body back to optimal condition, aka the norm
3. corrective actions are carried out by effectors (glands/muscles)
4. when conditions are restored back to norm, a negative feedback is sent back to the control centre via receptors to prevent further corrective actions
why is the presence of glucose in urine a sign of diabetes? what are the effects of high concentration of glucose in urine?
in patients with diabetes, elevated blood glucose exceeds the reabsorption capacity of the kidneys, causing glucose to remain in the filtrate
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1. high concentration of glucose in urine = more water excreted along with it = excessive volumes of urine and persistent thirst
2. insufficient glucose available to meet the needs of most body cells = fat becomes the main substrate for cellular respiration
describe the hemodialysis process
1. blood is drawn from fistula in patient's arm and pumped through a dialysis machine
2. in dialysis machine, blood is passed through a dialyser, which contains many tubing that have partially permeable walls
3. dialysis fluid introduced into dialyser and be in contact with tubing, where diffusion of waste materials from blood into dialysis fluid occurs
4. small molecules such as urea and other metabolic waste products diffuse out of tubing into dialysis fluid; blood cells, platelets, other large molecules remain in tubing
5. blood then returned through fistula in patient's arm
describe phagocytes (characteristics + function), phagocytosis, and phagocyte action
phagocytes:
- irregular shapes
- lobed nucleus so it can move
- changes shape and can squeeze through capillary walls
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functions to engulf and ingest foreign particles by phagocytosis
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phagocytosis refers to the process of engulfing and ingesting foreign particles by phagocytes (in process of fighting bacteria, some phagocytes are killed by bacteria, forming pus)
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1. phagocytes are attracted to infection sites/wounds by chemical messages
2. recognises pathogen and forms pseudopodia to enclose it
3. vesicle is formed, separating from cell membrane and into cytoplasm
4. vesicles formed fuse w lysosomes, hydrolytic enzymes in lysosomes digest engulfed pathogen
5. phagocyte may absorb digested products and use for own metabolism
contents of dialysis fluid
- contains same concentration of essential substances (e.g. glucose, amino acids, salts) as healthy blood so that essential substances will not diffuse out of blood to dialysis fluid
- if person lacks essential substances, substances in dialysis fluid can diffuse into blood
- does not contain metabolic waste products = sets up suitable concentration gradient for waste products (urea, uric acid, creatinine, excess salts) to diffuse out of tubing into dialysis fluid = maintains correct solute concentration and water potential of blood
what happens when body temperature increases beyond norm? (9)
1. thermoreceptors located in the hypothalamus detect internal temperature changes by monitoring the temperature of the blood flowing through it / thermoreceptors located in the skin detect external temperature changes
2. thermoreceptors send nerve impulses to the hyothalamus
3. hypothalamus sends nerve impulses to the various effectors for them to carry out corrective actions
4. vasodilation of arterioles occurs, allowing more blood to flow into the capillaries near the skin surface, and thus more heat to be lost to the surroundings by conduction, convection, and radiation
5. sweat glands become more active, sweat production increases, water in sweat evaporates, latent heat of vapourisation removed from body
6. erector muscles relax, hair shafts flatten and allow free circulation of air above airs; the moving air conducts heat away from the body
7. metabolic rate (liver) decreases, leading to less heat being released
8. body temperature decreases back to norm
9. negative feedback is sent to control centre via receptors to stop further corrective actions
describe the effects of adrenaline secretion in the liver/muscles, liver, heart, lungs, arterioles in skin, and pupils
- liver and muscles are stimulated, and breakdown of glycogen into glucose is sped up, leading to increased blood glucose levels
- liver is stimulated, and metabolic rate is increased, leading to more energy being released by tissue respiration
- heart is stimulated, increasing heartbeat rate and blood pressure, leading to oxygen and glucose being carried faster to the muscles
- (lungs) rate and depth of ventilation increased, leading to more oxygen being taken in
- arterioles in skin contract, causing paleness and channeling more blood to muscles
- pupils dilate and vision is enhanced
describe the process of selective reabsorption in the kidneys
selective reabsorption refers to the transport of useful substances from the filtrate back into the blood.
1. proximal convoluted tubule
- (healthy person) all glucose, amino acids, and vitamins are reabsorbed into the surrounding capillaries through the walls of the nephron
- 85% of sodium ions, chloride ions, and water are reabsorbed
- active uptake of the ions increases the water potential of the filtrate in the nephron
- water is reabsorbed by osmosis
2. loop of Henle
- sodium and other ions and water are reabsorbed
3. distal convoluted tubule
- water and a smaller concentration of ions are reabsorbed
4. collecting duct
- remaining water as required by the body is reabsorbed
describe coronary heart disease and what would happen if the coronary artery were to be completely blocked
- coronary arteries branch out from aorta to provide oxygen and nutrients to heart muscles to sustain it for contractions
- plaque narrows lumen of arteries, reducing amount of oxygen and nutrients being supplied to heart muscles
- pressure higher due to plaque since liquid is incompressible and same volume of blood must go through to reach cells
- if pressure too high, blood vessel may burst
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- myocardial infarction may occur aka heart attack
- heart tissue does not get enough oxygen and nutrients, tissue dies, causing damage to heart
- infarction may disrupt conduction system of heart and cause sudden death to patient
describe the similarities and differences between nervous coordination and hormonal coordination (2+5)
1. both provide pathways of communication within the body to coordinate various activities
2. both involve transmission of messages to effectors
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1. nature of message
nc: nerve impulses are electrical and neurotransmitters are chemical
hc: hormones are chemical
2. route of transmission
nc: along neurones
hc: in bloodstream
3. rate of transmission
nc: rapid
hc: relatively slow
4. areas affected
nc: restricted to structures linked to related neurones
hc: over many parts of the body
5. duration of effect
nc: generally short-lived
hc: generally long-lasting
what happens when body temperature decreases beyond norm? (10)
1. thermoreceptors located in the hypothalamus detects internal temperature changes by monitoring temperature of the blood flowing through it / thermoreceptors located in the skin detect external temperature changes
2. thermoreceptors send nerve impulses to the hypothalamus
3. hypothalamus sends nerve impulses to various effectors to carry out corrective actions
4. vasoconstriction of arterioles occurs, allowing less blood to flow through capillaries near skin surface, allowing less heat to be lost to the surroundings via conduction, convection, and radiation
5. sweat glands become less active, sweat production decreases, skin surface comparatively dry, no evaporation, no cooling effect
6. erector muscles contract, hair shafts become perpendicular to skin surface to trap air, retaining heat to keep the skin warm since the trapped air is a poor conductor of heat
7. metabolic rate (liver) increases, releasing more heat
8. skeletal muscles undergo spasmodic contraction, which releases heat due to muscle respiration to release energy for contractions
9. body temperature increases back to norm
10. negative feedback to sent to the control centre via receptors to stop further corrective actions
what happens when blood glucose concentration increases beyond norm?
1. pancreas detects stimulus and secretes more insulin into the blood
2. blood transports insulin to body cells, liver, and muscles
- this promotes the uptake of glucose by almost all body cells especially liver, muscles, and adipose tissue (except the brain as it does not store glycogen)
- stimulates liver and muscle to convert excess glucose to glycogen
3. blood glucose concentration decreases back to norm
4. negative feedback is sent to pancreas to prevent further corrective action
describe the ultrafiltration process
1. renal artery splits into numerous arterioles, each leading into a nephron, where each arteriole then splits into the glomerulus
2. the lumen of the afferent arteriole, which brings blood into the glomerulus, is larger than the lumen of the efferent arteriole, which brings blood away
a. blood flows more readily into the glomerulus through the wider afferent arteriole than it can leave through the narrower efferent arteriole, causing blood to dam up in the glomerulus, creating high blood pressure, which provides the main force required for the filtering process
b. the high blood pressure forces blood plasma into the lumen of the Bowman's capsule along the entire length of the glomerulus
3. blood plasma contains water and small molecules (ie glucose, amino acids, minerals, and nitrogenous products) which form the filtrate
4. blood cells, platelets, and large molecules (ie blood proteins and fats) remain in the blood and leave the glomerulus via the efferent arteriole
describe the cardiac cycle
1. atrial systole
- atria contract and force remaining blood through the atrioventricular valves into the ventricles
2. atrial diastole
- occuring simultaneously as ventricular systole, atria relax
- blood from pulmonary vein/vena cava start filling up atria
3. ventricular systole
- ventricles contract
- pressure in ventricles rise
- pressure of blood pushes atrioventricular valves upwards, forcing them shut
- produces a "lub" sound
- when ventricular pressure higher than aortic/pulmonary artery pressure, semi-lunar valves open
- blood in ventricles enter aorta/pulmonary artery
4. ventricular diastole
- ventricles relax
- pressure in ventricles decrease
- allows backflow of blood from aorta/pulmonary artery towards ventricles
- backward flow of blood closes semi-lunar valves
- produces a "dub" sound
- as ventricles continue to relax, pressure falls too quickly
- when ventricular pressure drops below atrial pressure, AV valves open, blood flows into ventricles
describe double circulation and its function
1. blood passes through the heart twice in one complete circuit
2. pulmonary circulation at lower pressure
- blood enters lungs at lower pressure compared to blood leaving the heart
- ensures that blood flows more slowly through the lungs, allowing sufficient time for blood to be well-oxygenated before returning to the heart
3. systemic circulation at higher pressure
- ensures oxygenated blood is distributed to other body tissues more quickly
- helps to maintain high metabolic rate in mammals
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- ensures complete separation of oxygenated and deoxygenated blood
- ensures only oxygenated blood reaches cells
- provides efficient transport of oxygenated blood