Human Physiology Flashcards
annotate digestive system
mouth
ingestion and chewing (saliva)
mouth
ingestion and chewing (salvia)
stomach
killing pathogens in food and protein digestion
gall bladder
stores bile (fluid that aids digestion)
liver
secretes bile
pancreas
secretes digestive enzymes
small intestine (structure and function)
digestion and absorption
- layers of folded tissue
- serosa — an outer coat
- longitudinal muscle layers
- circular muscles layer
- sub-mucosa — a tissue layer containing blood and lymph vessels
- mucosa — the lining of the small intestine, with the epithelium that absorbs nutrients on its inner surface
large intestine
absorption of water
anus
egestion of feces
peristalsis and digestion in small intestine (enzymes secreted)
Waves of contraction of longitudinal muscle, called peristalsis:
- moves food along the intestine
- prevents backflow of food towards the mouth
- (together with horizontal muscles) mixes food with enzymes in the small intestine
Enzymes digest most macromolecules in food into monomers in the small intestine (e.g. proteins, starch, glycogen, lipids and nucleic acids). Cellulose remains undigested. The pancreas secretes three types of enzyme into the lumen of the small intestine:
digestion of starch
There are two types of molecules in starch: amylose and amylopectin.
Amylase breaks 1,4 bonds in chains of four or more glucose monomers, so it can digest amylose into maltose but not glucose. Because of the specificity of its active site, amylase cannot break the 1,6 bonds in amylopectin. Fragments of the amylopectin molecule containing a 1,6 bond that amylase cannot digest are called dextrins.
Digestion of starch is completed by enzymes in the membranes of microvilli on vilus epithelium cells: maltase and dextrinase digest maltose and dextrins into glucose. Also, in the membranes of the microvilli are protein pumps that cause the absorption of the glucose produced by digesting starch.
Blood carrying glucose and other products of digestion flows though villus capillaries to venules in the submucosa of the wall of the small intestine. The blood in these venules is carried via the hepatic portal vein to the liver, where excess glucose can be absorbed by liver cells and converted to glycogen for storage.
villi and epithelium (structure and function)
Villi increase the surface area of epithelium over which nutrient absorption is carried out.
epithelium = single layer of cells, either microvilli or globet cells that secrete mucus forming the inner lining of the mucosa
inside the villi = blood capillaries and lymphatic system (lacteal)
The rate of absorption depends on the surface area of this epithelium. (The adult small intestine is ca 7 meters long and 25-30 millimeters wide. Villi absorb mineral ions and vitamins and also monomers formed by digestion such as glucose.)
methods of absorption + the nutrients using the specific transport
simple diffusion: hydrophobic nutrients such as fatty acids and monoglycerides
facilitated diffusion (channel proteins): hydrophilic nutrients such as fructose
active transport: mineral ions such as sodium, calcium and iron
endocytosis (pinocytosis): triglycerides and cholesterol in lipoprotein particels
More complex transport methods include how glucose is absorbed by sodium co-transporter proteins, which move a molecule of glucose together with a sodium ion across the membrane together into the epithelium cells. The sodium gradient is generated by active transport of sodium out of the epithelium cell by a protein pump. (The glucose can be moved against its concentration gradient because the sodium ion is moving down its concentration gradient.)
Modeling absorption with dialysis tubing
Cola drink contains a mixture of substances which can be used to model digested and undigested foods in the intestine. The water outside the bag is tested at intervals to see if substances in the cola have diffused through the dialysis tubing.
The expected result is that glucose and phosphoric acid, which have small-sized particles, diffuse through the tubing but caramel, which consists of larger polymers of sugar, does not.
Harvey and the circulation of blood
Until the 17th century the doctrines of Galen, an ancient Greek philosopher, about blood were accepted with little question by doctors. Galen taught that blood is:
- produced by the liver
- pumped out by the heart
- consumed in the other organs.
William Harvey is usually credited with the discovery of the circulation of blood. He demonstrated that blood flow through vessels is unidirectional with valves to prevent back flow and also that the rate of flow through major vessels is far too high for blood to be consumed in the body after being pumped out by the heart. He showed that the heart pumps blood out in arteries and that it returns in veins.
He also predicted the existence of capillaries that linked arteries to veins but where too small to be seen with his contemporary equipment.
The double circulation (pulmonary and systemic ciruclation)
pulmonary circulation goes to the lungs
systemic circulation goes to other organs
The heart is a double pump with left and right sides. The right side pumps deoxygenated blood to the lungs via the pulmonary artery. Oxygenated blood returns to the left side of the heart in the pulmonary vein. The left side pumps this blood via the aorta to all organs of the body apart from the lungs. Deoxygenated blood is carried back the right side of the heart in the vena cava.
types and structure of blood vessels
arteries convey blood pumped out at high pressure by the ventricles from the heart away. They carry the blood the tissues of the body
capillaries carry blood through tissues. They have permeable walls that allow exchange of materials between the cells of the tissue and the blood in the capillary
veins collect blood at low pressure from the tissues and return it to the atria of the heart
Cardiac muscle and coronary capillaries
The walls of the heart are made of cardiac muscle – it can contract on its own without being stimulated by a nerve (myogenic contraction).
There are many capillaries in the muscular wall of the heart. The blood running through these capillaries is supplied by the coronary arteries, which branch off the aorta, close to the semilunar valve. The blood brought by the coronary arteries brings nutrients and oxygen for aerobic cell respiration, providing energy for cardiac muscle contraction.
annotate
cardiac cycle (beating of the heart) + pressures during phases
- The walls of the atria contract, pushing blood from the artria into the ventricles through the atria-ventricular valves, which are open. The semilunar valves are closed, so the ventricles fill with blood.
- The walls of the ventricles contract powerfully and the blood pressure rapidly rises inside them. This first causes the atria-ventricular valves to close, preventing back-flow to the atria and then causes the semilunar valves to open, allowing blood to be pumped out into the arteries. At the same time the artria start to refill by collecting blood from the veins.
- The ventricles stop contracting so pressure falls inside them. The semilunar valves close, preventing back-flow from the arteries to the ventricles. When the ventricular pressure drops below the atrial pressure, the atrio-ventricular valves open. Blood entering the atrium from the veins then flows on to start filling the ventricles.
The next cardiac cycle begins when the walls of the atria contract again.
Control of heart rate
and
Changes in the rate
Sinoatrial (SA) node — one region of specialized cardiac muscle cells in the wall of the right atrium acts as the pacemaker of the heart by initiating each contraction. The node sends out an electrical signal that stimulates the contraction as it is propagated first through the walls of the atria and then through the walls of the ventricles.
Change in heart rates (messages) can be carried to the SA node by nerves and hormones.
- Impulses brought from the medulla of the brain by two nerves can cause the SA node to change the heart rate. One nerve speeds up the rate and the other slows it down.
- The hormone adrenalin (epinephrine) increases the heart rate to help prepare the body for vigorous physical activity.
Coronary artery disease (description and causes)
Coronary arteries are arteries surrounding the heart.
Is caused by fatty plaque building ip in the inner lining of coronary arteries, which become occluded (narrowed). As this becomes more severe, blood flow to cardiac muscle is restricted, causing chest pain. Minerals often become deposited in the plaque making it hard and rough. Various factors have been shown by surveys to be associated with coronary artery disease and are likely causes of it:
- high blood cholesterol levels
- smoking
- high blood pressure (hypertension)
- high blood sugar levels (diabetes)
- genetic factors (thus a family history of the disease)
Barries to infection (and defences if the barriers are trespassed)
A pathogen is an organism or virus that causes disease.
Primary defenses are barriers:
- Skin; sebaceous glands in the skin secrete lactic acid and fatty acids, which make the skin acidic. This prevents, very effectively, the growth of most pathogenic bacteria.
- Mucous membranes (“Schleimhaut”) are soft areas of skin that are kept moist with mucus, found in the nose, trachea, vagina and urethra. Many bacteria are killed by lysozyme, an enzyme in the mucus, or get caught in the sticky mucus in the trachea; cilia then push the mucus and bacteria up and out of the trachea.
When pathogens enter the body:
two types of white blood cells fight infections: phagocytes and lymphocytes.
When pathogens enter the body:
two types of white blood cells fight infections:
phagocytes and lymphocytes.
Phagocytes
Phagocytes ingest pathogens by endocytosis. The enzyme lysosome then kills and digests the pathogens. This ingestion can occur in blood but also at the immediate site of infection in tissue. Large number of phagocytes at a site form pus.
Phagocytes give humans non-specific immunity to diseases, because a phagocyte does not distinguish between pathogens — it ingests any pathogen if stimulated to do so.
Blood clots in coronary arteries
If the deposits of plaque in coronary arteries rupture, blood clots form (coronary thrombosis), which may completely block the artery. Consequentially, an area of cardiac muscle receives no oxygen and stops beating in a coordinated way — a heart attack. Uncoordinated contraction of cardiac muscle is fibrillation. This may be fatal, or the heart starts beating again.
annotate ventilation system
muscles used in ventilation
Antagonistic muscles are required for inspiration and expiration because muscles only work when they contract, forcing air in and out of the lungs.
Inhaling
- The external intercostal muscles contract, moving the ribcage up and out.
- The diaphragm contracts, becoming flatter and moving down.
- The muscle moments increase the volume of the thorax.
- The pressure inside the thorax therefore drops below atmospheric pressure.
- Air flows into the lungs from outside the body until the pressure inside the lungs rises to atmospheric pressure.
Exhaling
- The internal intercostal muscles contract, moving the ribcage down and in.
- The abdominal muscles contract, pushing the diaphragm up into a dome shape.
- The muscle movements decrease the volume of the thorax.
- The pressure inside the thorax therefore rises above atmospheric pressure.
- Air flows out from the lungs to outside the body until the pressure inside the lung falls to atmospheric pressure.
Adaptions of an alveolus for gas exchange (pneumocytes)
- permeable to oxygen and carbon dioxide
- a large surface area for diffusion
- thin, so distance for diffusion is small
- moist, oxygen can dissolve
- as the lung contains hundreds of millions of alveoli, a huge surface area is available
Type 1 pneumocytes
Extremely thin (single layer) and permeable alveolar cells that are adapted to carry out quick gas exchange.
Type 2 pneumocytes
Secrete a fluid to keep the inner alveolus wall surface moist and allow gases to dissolve. The fluid also contains a natural detergent (“cleaner” - surfactant), to prevent the sides of the alveoli from sticking together by reducing surface tension.
Blood capillaries
A dense network of capillaries with low oxygen and high carbon dioxide blood concentrations.
emphysema
The main cause of emphysema are smoking and air pollution. The cilia that line the airways and expel mucus are damaged, so mucus builds up in the lungs, causing infections. Toxins in cigarette smoke and polluted air cause inflammation and damage to the white blood cells that fight infections. A protease (trypsin) is released from inflamed cells and damaged white blood cells. This enzyme digests elastic fibers in the lungs and eventually causes complete breakdown of alveolus walls. Microscopic alveoli are replaced by progressively larger air sacs with thicker, less permeable walls.
Emphysema is a chronic and progressive disease with severe consequences. As the surface area for gas exchange is reduced, the oxygen saturation of the blood falls and exercise becomes more difficult. The lungs lose their elasticity, making it increasingly difficult to exhale (shortness of breath). Mucus in the lungs causes coughing and wheezing (“schnaufen”).
Structure and function of neurons
The nervous system is composed of cells called neurons. They carry messages at high speed in the form of electrical impulses. Many neurons are very elongated and carry impulses long distances in a short time.
Myelinated nerve fibers have a myelin sheath with small gaps called nodes of Ranvier, allowing the nerve impulse to jump from node to node. This is know as saltatory conduction and speeds up the transmission along the axon.
functioning of synapsis (outline)
- A nerve impulse reaches the end of a pre-synaptic neuron.
- Depolarization of the pre-synaptic membrane causes vesicles of neurotransmitter to move to the pre-synaptic membrane and fuse with it, releasing the neurotransmitter into the synaptic cleft by exocytosis.
- The neurotransmitter diffuses across the synaptic cleft and binds to receptors in the post synaptic membrane.
- The receptors are transmitter-gated sodium channels, which open when neurotransmitter binds. Sodium ions diffuse into the post-synaptic neuron. This causes depolarization of the post-synaptic membrane.
- The depolarization passes on down the post-synaptic neuron as an action potential.
- Neurotransmitter in the synaptic cleft is rapidly broken down, to prevent continuous synaptic transmission.
action potentials
The depolarization and repolarization of a neuron, due to facilitated diffusion of ions across the membrane through voltage-gated ion channels.
If the potential across the membrane rises from -70 to -50mV (threshold potential), voltage-gated sodium channels open and sodium ions diffuse in down the concentration gradient. The entry of positively charged sodium ions causes the inside of the neuron to develop a net positive charge compared to the outside — the potential across the membrane is reversed — depolarization.
The reversal of membrane polarity causes potassium channels to open, allowing potassium ions to diffuse out down the concentration gradient. The exit of positively charged potassium ions causes the inside of the neuron to develop a net negative charge again compared with the outside — the potential across the membrane is restored — repolarisation.
osciloscope traces
The changes in membrane potential in axons during an action potential can be measured using electrodes, displayed on an oscilloscope.
- The axon membrane rises from resting to threshold potential, either due to local currents or to the bind of a neurotransmitter at a synapse — stimulus.
- Membrane depolarizes due to voltage-gated sodium channels opening.
- Membrane repolarises due to voltage-gated potassium channels opening.
- Membrane returns to the resting potential due to the active pumping of Na+ ions out and K+ ions in to the axon.
thyroxin (composition, where is it secreted and why)
hormone regulating: metabolic rate & body temperature
- targets almost all cells.
- Higher metabolic rates support more protein synthesis and growth and it increases the generation of body heat.
- Thyroxin is implicated in heat generation by shivering and uncoupled cell respiration in brown adipose tissue (BAT) — secreting more thyroxin.
- It also causes constriction of vessels that carry blood from the core to the skin, reducing heat loss.
- Secreted by the thyroid gland in the neck.
- It has an unusual chemical structure as it contains four atoms of iodine.
- Prolonged deficiency of iodine in the diet therefore prevents the synthesis of thyroxin.
annotate (with function) female reproductive system
annotate (with function) male reproductive system
outline of menstruation
- FSH rises to a peak towards the end of the menstrual cycle and stimulates the development of follicles, each containing an oocyte and follicular fluid. FSH also stimulates secretion of oestrogen by the follicle wall.
- Oestrogen rises to a peak towards the end of the follicular phase. It stimulates the repair and thickening of the endometrium after menstruation and an increase in FSH receptors that make the follicles more receptive to FSH, boosting oestrogen production (positive feedback). When it reaches high levels oestrogen inhibits the secretion of FSH (negative feedback) and stimulates LH secretion.
- LH rises to a sudden and sharp peak towards the end of the follicular phase. It stimulates the completion of meiosis in the oocyte and partial digestion of the follicle wall allowing it to burst open at ovulation. LH also promotes the development of the wall of the follicle after ovulation into the corpus luteum which secretes oestrogen (positive feedback) and progesterone.
- Progesterone levels rise at the start of the luteal phase, reach a peak and then drop back to a low level by the end of this phase. Progesterone promotes the thickening and maintenance of the endometrium. It also inhibits FSH and LH secretion by the pituitary gland (negative feedback).
