6. HUMAN PHYSIOLOGY Flashcards
Explain how the release of gastric juice is controlled in the human body.
- release of gastric juice is controlled by the nervous and hormonal system
- smell and sight of food sends an impulse to the brain
- an impulse causes parietal cells to release gastric juice
- chemoreceptors in the stomach sense the food and stretch receptors sense the stretching of the stomach, impulse is sent to the brain
- brain sends an impulse via the vagus nerve to endocrine cells in the stomach to release gastrin hormone
- gastrin stimulates further the production of gastric juice
- when the pH falls to low (sensed by chemoreceptors) brain sends a signal to release somatostatin hormone which inhibits the release of stomach acid
- when chyme moves to the small intestine pancreas releases digestive juices that have bicarbonate ions that neutralize stomach acid
- liver exretes bile that emulsifies fats
Explain the roles of specific hormones in the menstrual cycle, including positive and negative feedback mechanisms.
[8]
- anterior pituitary secretes FSH which stimulates follicle development
- follicles secrete estrogen
- estrogen stimulates more FSH receptors on follicle cells
- positive feedback on pituitary which releases more FSH and (since FSH develops follicles and follicles produce estrogen –> more estrogen)
- estrogen promotes development of endometrium
- estrogen stimulates LH secretion
- LH cause ovulation
- LH results in negative feedback on follicle cells/estrogen production
- LH causes follicle to develop into corpus luteum
which produces progesterone - progesterone thickens the uterus lining
- high progesterone results in negative feedback on LH secretion
- if no fertilisation progesterone levels drop and allow FSH secretion
- falling progesterone leads to menstruation
Explain how an impulse passes along the axon of a neuron. [8]
- impulse is an action potential that is propagated throughout the axon
- neurotransmitter attaches to the receptor initiating the impulse
- resting potential (-70mV) is negative inside and positive outside the membrane
- for every 2 K+ pumped in, 3Na+ are pumped out
- if neuron is stimulated threshold potential of –50mV is reached
- voltage gated sodium channels open and Na+ diffuse in
- it causes the depolarization of the membrane (from -70mV to 40mV)
- local currents cause depolarization in adjecent part of the axon
- repolarization of the neuron happens when potassium channels open and K+ diffuse out
- Na+/K+ pump restores resting potential
- myelin around the axon speeds up the transmission as it allows for saltatory conduction
All motor neurons use acetylcholine to activate skeletal muscle. Explain the effect of neonicotinoid pesticides in insect synapses in the central nervous system. [3]
- Bind to acetylcholine receptors
- binding is irreversible
- Prevents acetylcholine binding
- muscle contraction blocked
which causes paralysis
Which cells produce insulin?
Beta cells of the pancreas
Explain the propagation of nerve impulses along the membrane of a neuron [3]
a. depolarization of part of axon/membrane triggers/causes depolarization of next part;
b. local currents;
c. diffusion of sodium ions between depolarized part and next/polarized part (of axon);
d. resting potential reduced/polarization of membrane becomes less /change from -70 to -50mV;
e. sodium channels open when -50mV/threshold potential reached;
f. entry of sodium ions causes depolarization;
g. saltatory conduction in myelinated neurons/axons
Explain the process of synaptic transmission.
- depolarization of pre-synaptic membrane
- Ca 2+ ions diffuse into the neuron
- vesicles with neurotransmitters exit by exocytosis
- neurotransmitter diffuses and reaches post-synaptic membrane receptors
- neurotransmitter inititates an impulse
- enzymes break down the neurotransmitter
What organ secretes insulin and glucagon?
Insulin and glucagon are secreted by β and α cells of the pancreas respectively to control blood glucose concentration.
Which organ secretes thyroxin and what is its function?
Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature.
Where is leptin secreted and what is its function?
Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite.
What secretes melanin and what is its function?
- Melatonin is secreted by the pineal gland to control circadian rhythms
- melanin production is controlled by amount of light detected by the retina
- high production/secretion in the dark
What is the cause of type I diabetes?
destruction of beta cells of pancreas
Outline the functions of the structures in female reproductive system.
Ovary - Produce eggs, estrogen and progesterone
Oviduct - Collect eggs at ovulation, provide a site
for fertilization then move the embryo to the
uterus
Uterus - Provide for the needs of the embryo and
then fetus during pregnancy
Cervix - Protect the fetus during pregnancy and then
dilate to provide a birth canal
Vagina - Stimulate penis to cause ejaculation and
provide a birth canal
Vulva - Protect internal parts of the female
reproductive system
Name the structure of male reproductive system and state their function
Testis - Produce sperm and testosterone
Scrotum - Hold testes at lower than core body
temperature
Epididymis - Store sperm until ejaculation
Sperm duct - Transfer sperm during ejaculation
Seminal vesicle
and prostate
gland -
Secrete fuid containing alkali,
proteins and fructose that is added
to sperm to make semen
Urethra - Transfer semen during ejaculation
and urine during urination
Penis - Penetrate the vagina for ejaculation
of semen near the cervix
Explain how gas exchange is maintained in the human respiratory system.
- ventilation is the process of inhaling fresh air into the lungs and exhaling stale air from lungs
- movement of air due to pressure gradient due to volume changes of the thorax
- external intercostal muscles and diaphragm contract expanding the thorax
- internal intercostal muscles and abdominal muscles contract forcing the air out
- exchange of oxygen and carbon dioxide is possible due to concentration gradient maintained by blood pumping by the heart
- CO2 diffuses out of the blood to the alveoli, 02 from the lungs to the blood
-pneumatocytes I are very thin so small distance between capillaries and alveoli, fast diffusion - network of capillaries
- high surface area of the lungs
- pneumocytes II secrete surfactants which prevent alveoli from collapsing
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