Trimester Revision Flashcards
(131 cards)
1
Q
What is plasma?
A
Liquid with sugar, water, proteins, hormones and salt. Proteins establish an osmotic gradient between blood and interstitial fluids to buffer pH.
2
Q
What is a hematocrit?
A
The % of total blood volume occupied by cell components (red blood cells)
3
Q
What are the three proteins within plasma?
A
- Albumins - contribute to osmotic pressure
- Globulins (alpha,beta,gamma)- transport, help blood clotting, act as antibodies
- Fibrinogen - helps blood clotting
4
Q
All about erythrocytes:
A
Red blood cells. Have quaternary structure as they have four hemoglobin chains that carry oxygen. Can play a role in pH buffering as they can also bind with CO2, CO and NO, H+. Do not have any organelles and are biconcave.
5
Q
Why do RBC have a biconcave shape?
A
Increases surface area for diffusion of oxygen.
6
Q
What are leukocytes?
A
White blood cells.
7
Q
What are thrombocytes?
A
Platelets. Plug wounds to stop bleeding and are formed from megakaryocytes in the bone marrow.
8
Q
Blood life cycle:
A
Kidney detects low blood oxygen, releases erythropoietin to the bone marrow, stimulating it to make more red blood cells.
9
Q
List the leukocytes from most to least common:
A
Use acronym Never Let Monkeys Eat Bananas. Neutrophils, leukocytes, monocytes, eosinophils and basophils.
10
Q
What is characteristic of anemia?
A
Reduced oxygen carrying capacity of the blood = lower numbers of RBCs.
11
Q
Normal hematocrit % for women and men?
A
Women: 42%
Men: 45%
12
Q
What happens when we have lower numbers of red blood cells in the body?
A
A patient may be pale and feel tired. RBC carry oxygen to cells that will use it to make ATP. Less cells = less oxygen = less ATP = less energy for the patient.
13
Q
Why do bruises change colour?
A
Impact trauma will cause blood to leak below the skin surface from a damaged blood vessel. Different bruise colours occur as old red blood is engulfed by macrophages, stripping haem of iron and making it into biliverdin, which has a green colour. This will be converted to bilirubin which is orange/yellow. This will then combine with albumin and be transported to the liver where it will be excreted
14
Q
What are the three steps of haemostasis?
A
- Blood vessel spasm
- Formation of platelet plug
- Coagulation of blood
Exposing blood to collagen in damaged vessels causes platelets to stick and produce chemicals that promote more platelet aggregation.
15
Q
Factors that determine blood flow:
A
- Blood vessel diameter- influences resistance.
2. Blood pressure- blood flows from high to low pressure, larger pressure gradient results in greater velocity of blood
16
Q
What is MAP?
A
Mean arterial pressure. The average pressure in the arteries during one cardiac cycle.
17
Q
What is systole?
A
Systole, period of contraction of the ventricles of the heart that occurs between the first and second heart sounds of the cardiac cycle (the sequence of events in a single heart beat). Systole causes the ejection of blood into the aorta and pulmonary trunk.
18
Q
What is diastole?
A
Diastole is when the heart muscle relaxes. When the heart relaxes, the chambers of the heart fill with blood, and a person’s blood pressure decreases.
19
Q
How is low MAP countered?
A
When blood pressure drops, baroreceptors stimulate action potential to the brain stem that cause an increase in sympathetic activity, in order to increase cardiac output and return MAP back to normal.
low MAP causes a cascade that quickly increases sympathetic activation return MAP back to normal, causes increases firing of the SA node and contractility of the heart (higher heartrate) as well as increased venous return which causes a higher stroke volume. Through sympathetic stimulation and increase/decrease of parasympathetic influence MAP is brought back to normal. Sympathetic stimulation causes vasoconstriction which effects total peripheral resistance.
20
Q
Haematocrit for men and women:
A
women 42% and men 45%. Men have slightly higher haematocrits due to the hormone testosterone. Testosterone increases the production of erythropoietin (EPO), which is responsible for stimulating red blood cell production.
21
Q
What happens if there is a reduced number of red blood cells inn the blood?
A
Erythropoiesis occurs in the bone marrow and is controlled by erythropoietin (EPO). If the kidneys detect a reduced oxygen carrying capacity, which is associated with reduced RBC count, the kidneys will release EPO into the blood stream. EPO increases erythropoiesis, increasing the oxygen carrying capacity of the blood. This is a negative feedback loop
22
Q
What happens when we go from lying down to standing?
A
The gravitational force causes blood to pool at the veins in the leg. Decrease in venous return which results in lower blood pressure corrected by baroreceptor reflex. Increased heart rate compensates for lower blood pressure. Cardiac output decreases due to decrease in venous return. MAP will decrease as cardiac output will decrease. Systolic and diastolic pressure increases.
23
Q
Events occurring in a Wigger’s diagram/ one cardiac cycle?
A
First, the closing of the atrioventricular (AV) valves. Following the closure of the AV valves is a sharp rise in the ventricular pressure as isovolumetric ventricular contraction occurs.
Second, opening of the pulmonary and aortic semilunar vales. The pressure inside the ventricle is greater than in the aortic arch and pulmonary trunk, causing the semilunar valves to open, allowing blood to exit the heart and enter the pulmonary and systemic circulation.
Finally, isovolumetric ventricular relaxation. Here, all the heart valves are closed - The pulmonary and aortic semilunar valves closed as pressure is greater in the pulmonary trunk and aortic arch than inside the ventricles. The ventricles are relaxing and pressure is decreasing in preparation for re-filling by the atria.
Once pressure inside the atria is higher than that in the ventricles, the AV valves will opens and blood will enter the ventricles.
24
Q
Finding ultrafiltration:
A
Pressure out of capillary - pressure into capillary = ultrafiltration pressure
25
ECG- what happens in each section?
| (P wave, QRS, T
P: atrial depolarisation
QRS: ventricular depolarisation
T: ventricular repolarisation
PR segment: AV nodal delay
ST segment: ventricles contracting and emptying
TP interval: ventricles relaxing and filling.
26
List the leukocytes from most to least common:
Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils (Never Let Monkeys Eat Bananas)
27
Example calculation- If 38 packed volume units of cells are separated from 51 volume units of plasma from a blood sample find haematocrit.
38+51=89, 38/89 x 100 = 42.6%
28
What are the symptoms of anemia and why do they occur?
A patient may feel tired and be pale when they have a lower RBC count as the cells contain haemoglobin that will carry oxygen to cells in the bpdy to make ATP. Lower oxygen carrying capacity of the blood gives a pale appearance (less red pigment from haemoglobin). Less oxygen means less ATP available = patient feels tired.
29
Why do bruises change colour?
A contusion is a bruise- it will change colour as impact trauma will cause blood to leak below the skin surface from damaged blood vessel. When old RBCs are engulfed by macrophages the haem will be stripped of iron and made into biliverdin, which is green in colour. Will convert to bilirubin which is orangey yellow and released to blood, then combines with albumin annd transported to liver where it will be excreted as urine or feces, giving each their colour
30
What are the three events occurring during haemostasis?
1. Blood vessel spasm
2. Formation of the platelet plug
3. Blood coagulation
Exposing blood to collagen in damaged vessels causes platelets to stick and produce chemicals that promote more platelet aggregation
31
What can happen if a mother's blood mixes with her fetuses positive blood type during birth if the mothers blood type is negative?
If a mother with negative blood group gives birth to a baby with positive blood group and is exposed to its blood supply when the placenta falls out (or something) the mother will produce D (Rh) antibodies if not treated. If she has another baby with positive blood type the antibodies will cross the placenta and destroy RBC of the fetus, lowering the hematocrit. Can cause anemia and be fatal
32
What is the process of a blood transfusion for doping?
Athlete will donate their blood which will be centrifuged. The liquid part will be re-injected and RBC's stored. Before the comp, RBCs will be re-injected to give more oxygen
33
What are the consequences of blood doping?
blood viscosity will increase, harder to pump blood. Risk of blood clot, causing stroke, heart attack or pulmonary embolism. Risk of infection if blood comes from someone else. If blood isn't matched correctly a transfusion reaction (agglutination) may occur.
34
What are reticulocytes and how do they relate to blood doping?
Reticulocytes are the final stage of RBC before full maturation, if there is a higher level of them in the blood it suggests that the bone marrow is being stimulated to release a higher amount of cells than normal
35
What is polycythemia?
When more RBC's are produced than destroyed. This is a primary condition. The secondary condition occurs when this is an appropriate response to a prolonged reduction of O2 delivery to tissues. common in people living at high altitudes.
36
What is the passage of a red blood cell through pulmonary and systemic circulation?
vena cava into right atrium and through right atrioventricular valve, pumped into pulmonary circulation through pulmonary artery. Pumped back into the heart through the pulmonary vein, enters left atrium and entering the left ventricle which it will then be pumped into systemic circulation by the aorta.
37
How do valves ensure one way movement of blood?
Valve leaflets point in the direction of blood flow and will open and close due to changes in blood pressure in front and behind the leaflets.
38
What is the structure of cardiac muscle cells?
Striated with intercalated discs. Discs connect neighboring cells to one another and have desmosomes that anchor. Gap junctions allows action potentials to pass between cells quickly. Allow muscle fibers to contract together. Arranged spirally in the heart allowing contraction and pumping in a wringing motion
39
What is the function of the pericardial sac?
Prevents friction of the heart against the lungs and prevents overfilling by restricting expansion.
40
How is electrical activity generated in the heart?
Positively charged ions (Na+) enter the cell, when a threshold crosses -55mv an action potential can occur, allowing lots of positive ions in, depolarizing the cell. After this repolarisation occurs, letting out potassium ions to rebalance. Action potential starts in SA node and spreads in both atria. The AV node is the only place an action potential can spread from atria-ventricle- it has an AV node delay by 0.1sec allowing atria to fully depolarize and contract. This signal moves down bundle of His and through myocardium via Purkinje fiber, which transmits rapidly to allow ventricles to contract as a unit.
41
How does the SA node work?
SA node = pacemaker potential. Slow depolarisation generated by protein transport pathways. Calcium enters and potassium leaves the channels. Funny sodium channels open during hyperpolarisation allowing sodium into the cell, allowing the cell to begin depolarising. T calcium channels open during depolarisation, allowing potential to cross the threshold, stimulating an action potential and the opening of L channels that allow this. At neutral membrane potential, calcium channels close and potassium channels open.
42
What happens during cardiac muscle action potentials?
There is no unstable membrane potential = this is a plateau phase. Electrical signal stimulates voltage gated sodium channels to open into the cell , stimulating depolarisation. Sodium channels close at above +30 membrane potential. Potassium channels will open, allowing repolarisation as potassium moves out of the cell.
43
Function of L type calcium channels in cardiac muscle:
Allow the plateau stage. Calcium moves into the cell, membrane potential stabilises. This increases the refractory period. After this, potassium channels open and let ions out.
L type calcium voltage gated channel will be open by action potentials, allowing calcium into cardiac muscle cells. Entry of calcium stimulates ryanodine calcium channels to then open, increasing calcium concentration in the cardiac muscle cell.
Calcium moves to contraction relaxation units in the muscle, binding to tryponin an actin filaments, enabling cross brisge cycling and contraction to occur. Calcium ions must enter from extracelluar fluid to trigger contraction. This provides 90-95% of calcium for contraction.
44
What is the refractory period of the heart?
Time period when a recently activated area is non responsive. In cardiac muscle, the refractory period is much longer as compared to skeletal muscle. Because of the refractory period, cardiac muscle cells cannot undergo tetanus, allowing sufficient pumping of blood throughout the body
45
What is isovolumetric ventricular contraction?
Period in cardiac cycle where there's a constant volume of blood in ventricles during contraction, resulting in ventricles contracting on fixed volume, increasing pressure. Both valves are closed.
46
The valves opening and closing during a cardiac cycle:
Ventricular filling occurs when pressure in the atria is greater than pressure in the ventricle, bicuspid AV valve is open and semilunar valve is closed. Isovolumetric contraction is reached when the AV valve closes. When blood pressure in ventricle is greater than in the aorta, the semilunar valve will open and systole will occur. As the process begins again, diastole occurs.
47
What are the lub dub sounds produced as a result of?
'lub' closure of AV valves, 'dub' closure of semilunar valves. Blood flow is laminar, which does not produce sound. Closing of the valves makes blood flow turbulent, which produces sound from vibrations
48
What is the SA node?
SA node is the pacemaker of the heart, influencing heart rate through consistent depolarization. Electric activity in the heart comes from pacemaker cells in the SA node. Heart is affected by the sympathetic and parasympathetic nervous systems. Their nervous systems don't generate electric activity - they modify it
49
How do parasympathetic nerves work?
The parasympathetic nerves have a longer preganglionic fiber and shorter postganglionic. The pre ganglionic fiber releases acetylcholine to nicotinic receptors on the postganglionic fiber. Acetylcholine from the post fiber binds to muscarinic receptors on the tissue site. The vagus nerve innervates the SA and AV node, decreases the heart rate and the rate at which the threshold is reaached. Potassium channels are stimulated to open more to counteract the effect of sodium and calcium entering the cell.
50
How do the sympathetic nerves work?
Sympathetic nerves have a shorter preganglionic fibre and a longer postganglionic fibre. Acetylcholine released from pre ganglionic to nicotinic receptors and adrenaline/noradrenalin released from the postganglionic fibre to bind with alpha or beta receptors. Innervates SA node, AV node and entire myocardium, increases the heart rate. Noredrenalin acts on sodium and calcium channels, stimulating them to open, generating more action potentials faster
51
What is atrial fibrillation?
Irregular, uncoordinated depolarization of atria. Problem starts in upper chambers of the heart, quivering (fibrillating) rather than beating, meaning that the heart doesn't pump blood as efficiently as it should. Catheter ablation can burn tissue that connects the pulmonary vein to atria with a laser, causing scar tissue that stops electric signaling from being directed to atria, stopping atrial fibrillation
52
Function of umbilical vein:
directs oxygen rich blood to the heart, diverting blood from liver and kidneys. A thicker wall is needed as blood pressure will be increased in a fetal circulatory system. This also makes vasoconstriction after birth easier
53
Function of foramen ovale:
foramen ovale connects the atria, allowing blood from right atria to move to the left during atrial contraction and through the aorta, which does not exist in adults. Blood that doesn't move through the foramen ovale, instead into the pulmonary trunk can pass through the ductus arteriosus to maximise the amount of oxygenated blood
54
Umbilical arteries function:
return to the placenta, dropping off its waste products. The cycle will then repeat.
55
Ductus venosus function:
connects umbilical vein to inferior vena cava, allows more blood to bypass hepatic circulation and the liver. Oxygen rich blood from placenta can move more directly to the heart.
56
Ductus arteriosus fuction:
protects lungs from circulatory overload, connects pulmonary artery to aorta resulting in more blood bypassing pulmonary circulation and not being pumped to the lungs (as they're filled with fluid). Has high pulmonary resistance, low pulmonary blood flow. Has blood with medium oxygen saturation
57
What happens to the ductus venosus and arteriosus after birth?
It constricts so that blood entering the liver is not bypassed. Lungs now used for oxygen uptake, causing vasoconstriction of ductus venosus and ductus arteriosus. Umbilical vein and arteries not required, vasocosntricting and becoming ligaments. Pulmonary resistance decreased. The right wall will be thicker than the left, hence the left wall will need about a month to thicken
58
What happens if ductus arteriosus doesn't close after birth?
patent ductus arteriosus can occur (extra blood being pumped to the lungs), more blood can enter pulmonary circulation and damage can occur to pulmonary vessels. If ductus arteriosus doesn't close, blood would flow backwards down into the lungs, resulting in a higher pressure in the lungs, could result in pulmonary oedema (hypoxic).
59
What happens if the foramen ovale doesn't close after birth?
patent foramen ovale can occur, as well as a greater volume of blood can enter pulmonary circulation and damage can be done to pulmonary blood vessels. Blood moves from right to left = great vol of blood in right side going to right ventricle, increasing volume and pressure of blood going to pulmonary circulation
This will cause more blood to go to the lungs, forcing fluid through the alveoli resulting in fluid in the lungs accumulating.
60
Steps in the use of a sphygmomanometer:
Wrap cuff around arm. Pump air into cuff to inflate it, putting pressure onto arm and stopping blood flow. Stethoscope will not pick up sound. Slowly release pressure, creating turbulent blood flow and a tapping sound in the stethoscope (first sound = systolic pressure). Pressure will be released further, causing muffled sounds (diastolic pressure).
61
What is pulse pressure?
Systolic minus diastolic pressure. If blood pressure = 120/80 then pulse pressure will be 40
62
Forces than influence fluid movement in and out of capillaries:
1. Capillary blood pressure (Pc) = fluid pressure exerted on the inside of capillary walls by the blood
2. Plasma colloid osmotic pressure = force exerted by plasma proteins (average 25 mmHg). Moves fluid into capillaries
3. Interstitial fluid hydrostatic pressure = pressure on outside capillary wall by interstitial fluid. Forces fluid into capillaries. (average 1mmHg)
4. Interstitial fluid-colloid osmotic pressure = in normal conditions this does not contribute significantly to bulk flow
63
When do ultrafiltration and reabsorption occur in the capillaries?
Ultrafiltration occurs when pressure inside the capillary is greater than pressure outside, pushing fluid out. Reabsorption occurs when inward driving pressures are greater than outward driving pressures, causing fluid to move into capillaries. This all occurs due to differences in hydrostatic and colloid osmotic pressures between plasma and interstitial fluid.
64
What is venous return?
volume of blood entering each atrium per minute from veins. Has mean pressure of 17mmHg. Atrial pressure will be near 0 which is still a good drivng pressure to move blood in the veins.
65
How can venous return be increased?
Venous return can be increased through sympathetic activity. vasoconstriction in veins will increase driving pressure toward the atria, increasing cardiac output. (vasodilation is not sue to more parasympathetic influence, it's due to LESS sympathetic influence)
66
What happens when arterioles vasoconstrict?
Vasocontriction in arterioles reduces flow, as resistance increases, while constriction in veins increases flow as more blood will be squeezed to the heart. Sympathetic influence can cause the same action BUT can have different outcomes
67
What is the skeletal muscle pump?
counters effects of gravity on the venous system- when lying down the force of gravity is uniform, but when standing this is not the case. Gravity will cause pressure to increase as we travel down the body (below the heart). Blood will accumulate in lower body, veins will expand and venous pooling will happen. A decrease in right ventricular pressure decreases stroke volume, decraese in left ventricular pressure reduces blood volume from pulmonary. This pump works to increase venous return.
68
How do veins counteract gravity?
They have valves that only allow blood to move forward+up. Valves will open when pressure behind is greater than in front.
69
The baroreceptor reflex in regulating blood pressure:
MAP constantly monitored by baroreceptors in the aortic arch and the neck/carotid sinus (pressure sensors) that continuously fire action potentials. Increase in arterial pressure = firing of action potential increases, and a decrease in pressure = decrease in action potential. The signals go to the cardiovascular control centre in the brain stem which will alter activity in sympathetic and parasympathetic input to heart and blood vessels. Baroreceptor reflex will increase sympathetic input to veins and arterioles to compensate for less venous return when standing.
Less sympathetic input will cause veins and arterioles to vasodilate, increasing venous pooling and the amount of blood going to organs. Cardiac output, venous return, stroke volume, cardiac output, blood pressure will all decrease.
70
In the baroreceptor reflex, what do the parasympathetic and sympathetic nervous systems interact with?
Para- SA node, AV node. Not veins and arterioles.
Symp- SA node, AV node, myocardium. Causes vasoconstriction that will increase blood pressure, resistance, heart rate, MAP and stroke volume. (Refer to equations)
71
Why do astronauts' faces puff up when they enter space?
facial puffiness is caused due to increased MAP in the head and chest. Blood volume will increase in these areas, this is called 'central pooling'. An increased end diastolic volume will increase stroke volume. If heart rate was the same then CO and MAP would increase due to the increased stroke volume, hence why the heart rate decreases. In the capillaries, more ultrafiltration will occur and less reabsorption
72
What is different in fetal circulation?
1. Lungs are not a gas exchange organ. Usually cardiac output from right side would all go to the lungs- in fetuses the ductus arteriosus will take blood from pulmonary trunk and directs it to the aorta instead of the lungs.
2. Umbilical vein runs through liver and joins to inferior vena cava, enters the right atrium. Blood with higher oxygen content will move across to the left atrium, to ventricle and out the aorta to the body (brain). Superior vena cava brings deoxygenated blood back to the heart.
3. Umbilical arteries take deoxygenated blood to the placenta and blood will be oxygenated and move back through the umbilical vein.
73
What happens if MAP increases above normal?
If MAP increases, the parasympathetic system will be stimulated. As blood pressure will have increased, the rate of action potential firing will also have increased. The CNS will stimulate the sympathetic system to be lowered and increase parasympathetic input. This input only increases at the heart, SA node and AV node, NOT veins and arterioles. The decrease in sympathetic input causes veins and arterioles to dilate, lowering stroke volume and total peripheral resistance. Heart rate will decrease, stroke volume will decrease and cardiac output will decrease at the heart, lowering MAP.
74
Platelet aggregation is reinforced by what signal?
thromboxane A2
75
Which is the correct sequence of events leading to clot formation?
prothrombin-->thrombin-->fibrinogen-->fibrin
76
What forms the meshwork of a clot?
fibrin
77
The right half of the heart pumps blood throught the __________ circuit and the left half pumps blood through the __________ circuit.
pulmonary;systemic
78
The sequence of contraction in the heart chambers is
both atria followed by both ventricles
79
A plateau phase in the action potential is found in and occurs because:
Ventricular cardiac muscle cells that contract. Caused by an influx of Ca2+ into the cell
80
What is stroke volume determined by?
Stroke volume is determined by the extent of venous return so part of this statement is correct. Parasympathetic influence heart rate but not force of contraction.
81
Explain Starling's Law of the Heart:
Is a length tension relationship in cardiac muscle that demonstrates the relationship between end diastolic volume and stroke volume. Can be influenced from input from the sympathetic nervous system. Cardiac muscle cells work at short sarcomere lengths (less than optimum overlap of the filaments) during resting conditions. Under the influence of sympathetic nerve stimulation a greater stroke volume will result at any end diastolic volume (up to that corresponding to optimum overlap of the contractile filaments). Cardiac muscle cells do not normally operate on the ascending limb of the curve.
82
What are veins?
Blood reservoirs.
83
Where is velocity of blood flow slowest?
Capillaries.
84
Function of the kidney
excretes waste, maintains water balance in the body, maintains blood volume, regulates concentration of ions in ECF, maintains osmolarity, maintains acid base balance, eliminates foreign compounds, secretes erythropoietin, secretes renin (salt conservation) and converts vitamin D into its active form.
85
The nephron in the kidney
There are two types of nephrons- cortical and juxtamedullary. The juxtamedullary has a longer Loop of Henle but the cortical nephron is present in higher levels
Vascular- blood supplied by afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries
Tubular- Bowman's capsule, proximal tubule, Loop of Henle, distal tubule, collecting ducts
86
Processes of urine production in the nephron
At glomerular capillaries, filtration occurs into Bowman's capsule. Non selective filtering process of everything that but plasma proteins and blood cells.
Tubular reabsorption from the proximal and the Loop of Henle into the peritubular capillaries. We reabsorb nutrients that we want to keep
Tubular secretion back into the distal tubule which will then be excreted as urine. Movement from plasma into tubular system.
87
Juxtaglomerular apparatus in the kidney
where tubular and vascular cells combine, secreting substances that control kidney function. Granular cells in blood vessels are specialised smooth muscle cells that secrete renin. Macular densa cells of the distal tubule detect salt levels and changes in salt levels, stimulating signal molecules that control filtration rate.
88
The three layers of glomerular membrane that act as a filter:
1. wall of glomerular capillary
2. acellular layer forming basement membrane
3. inner layer of Bowman's capsule, containing specialised cells, 'podocytes' that form filtration slits that form a sieve
89
Three forces in glomerular filtration
1. Glomerular capillary blood pressure (Pc)- force of blood on wall of glomerulus, pushes fluid out of the capillary, favoring filtration. Around 55mmHg which is higher than normal capillaries as the diameter of the afferent arteriole is larger than the efferent arteriole (efferent arterioles having high resistance). Hence more blood is entering, causes pressure on the capillaries as blood 'dams up', pushes blood to keep moving
2. Plasma colloid osmotic pressure (pi p)- plasma proteins can't be filtered, meaning plasma proteins are unequally distributed. Water will move by this gradient, moving from Bowman's capsule to glomerular capillaries. Opposes filtration at about 30mmHg
3. Bowman's capsule hydrostatic pressure- has fluid that exerts pressure at about 15mmHg into the capillaries. Opposes filtration.
90
Barriers that substances move through to be reabsorbed:
Luminal cell membrane, cytosol, basolateral, cell membrane, interstitial fluid, capillary wall
91
Passive reabsorption
no energy needed for substance transfer, substance moves down electrochemical or osmotic gradient
92
Active reabsorption
energy needed for transfer of substance in even one step, substance moved against gradient.
93
Na+ in the nephron
One of the most important substances reabsorbed by the nephron is Na. Will be reabsorbed across whole tubule but in different percentages. (67% proximal tubule, 25% loop of Henle, 8% distal and collecting tubule). This reabsorption is an active process, needs a Na K ATPase carrier. 80% of energy requirement for kidney goes to Na transport.
94
Proximal tubule
reabsorbs glucose, amino acids, water, Cl and urea.
95
Loop of Henle
regulates urine volume and concentration.
96
Distal and collecting tubules
control the amount of Na reabsorption and are controlled by hormones.
97
What is the RAAS system?
Renin Angiotensin Aldosterone System → regulates Na+, stimulating reabsorption in distal and collecting tubules.
98
How Na and Cl affect ECF:
Na and Cl account for >90% of ECF osmotic pressure (force that attracts and holds water). If Na increased, osmotic pressure increases meaning more water will be in ECF. If ECF expands then blood pressure will increase, if it decreases then BP decreases. Renin will be secreted by granular cells of juxtaglomerular apparatus when NaCl decreases in the distal tubule (detected by macula densa cells), or BP decreases in afferent arteriole
99
What does angiotensin do?
can increase the thirst response, stimulating an increase in fluid uptake. Can also cause arteriolar vasoconstriction, maximising water reabsorption by decreasing the amount of filtrate. Also acts on adrenal cortex, stimulating aldosterone release, causing an increase in Na reabsorption, thus increasing water reabsorption and ECF pressure.
100
How RAAS works:
Low blood pressure will be detected by the kidney. This will be due to a drop in Na concentration which will result in less water uptake and a reduced ECF. Juxtaglomerular apparatus detects lowered BP, secreting renin. Angiotensinogen is produced by the liver constantly- renin converts this to angiotensin-1. When this moves to the lungs, angiotensin converting enzyme (ACE) converts this to angiotensin-2. This compound stimulates the adrenal gland to produce aldosterone. Aldosterone will act on the collecting duct of the nephron, causing Na+ absorption. As a result more water will be up taken, increasing ECF and hence, blood pressure.
101
Role of aldosterone:
increases reabsorption in the distal tubule and the collecting duct.
102
What happens in space to an astronauts blood and urine?
In space, central pooling of blood in the upper body signals blood to push more blood through the heart, initially increasing stroke volume, end diastolic volume and cardiac output. Cardiac muscle cells will stretch with the increase of blood moving through. ANP (atrial natriuretic peptide) is a hormone that will be released from cells in the atria when the cardiac muscle cells stretch. This hormone opposes RAAS. Results in greater volume of urine excretion as it inhibits Na reabsorption in distal tubules and increases excretion of Na. Also dilates afferent arteriole increasing glomerular filtration rate.
103
What does ANP inhibit?
Two RAAS steps:
| secretion of renin from kidneys and aldosterone secretion from the adrenal cortex
104
Why do astronauts lose blood volume?
Increased fluid through increased stroke volume is interpreted as overhydration by the body, causing more fluid to be excreted as urine, resulting in astronauts to lose blood volume. The kidneys will control the increase in urine production. As less blood is available and more blood is being pushed, the heart rate will slow to compensate and reduce cardiac output. The baroreceptor reflex will have caused the heart to slow down after detecting an increase in MAP- it will try to decrease this.
105
Why are astronauts prone to fainting when returning to Earth?
Astronauts are prone to fainting when returning to Earth as there is lowered blood volume in the body, meaning that the baroreceptors find it hard to restore blood pressure. Less blood available means less oxygen can go to the brain, the body will right this by making us faint. RAAS will begin to cause fluid retention to restore blood volume.
106
vasopressin (ADH)
stimulates addition of aquaporin 2, a water channel into apical membrane of cells that line lumen collecting duct, so water can move from filtrate across cells into interstial fluid and into capillaries to produce concentrated urine. If we have too much water, vasopressin will not be present to produce a less dilute urine- water will be retained in the filtrate.
107
medullary countercurrent mechanism
vertical osmotic gradient in the medulla of each kidney is constantly maintained regardless of fluid in the body - the concentration of interstitial fluid increases from the cortex through the medulla. Juxtamedullary nephrons with the long loops of Henle establish the gradient and the vascular component, vasa recta maintains it. Collecting tubules use the gradient with vasopressin.
108
Loops of Henle and water permeability:
The decending loop of Henle is permeable to water (due to presence of aquaporins) and does not engage in transport of Na, hence if less water enters, fluid here will be more concentrated. The ascending Loop of Henle is always impermeable to water and will transport NaCl out of tubular lumen, making fluid more dilute as it moves up. This is a form of active transport that requires energy.
109
Why does the kidney concentrate the tubular fluid only to dilute it?
The vertical osmotic gradient is established in the medullary interstitial fluid. The gradient is used by the collecting duct to control the dilution of urine. The fluid will be hypotonic as it moves up the ascending tube, allowing more water to be excreted, decreasing water in ECF, maintaining blood pressure.
110
Why does the vertical osmotic gradient remain when fluid travels through the tubular system of a nephron?
Vasa recta maintains the gradient and renal medulla must receive blood to nourish tissues and transport water that is absorbed by the loops of henle. Blood flow through the medulla must not disturb the gradient and this is ensured by a hairpin loop in the vasa recta.
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Alveoli:
air pockets surrounded by elaborate capillaries, have thin walls so that the diffusion distance for gases is short =more efficient gas exchange. Slower air flow is needed in alveoli as we need time for gas exchange
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Conducting airways:
Trachea, bronchi, bronchioles. Bring air from environment into body, do not participate in gas exchange. Cartilage rings on the bronchi hold them open.
Deliver air to alveoli, warm and humidify air, removes foreign mater through sneezing and coughing.
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Trachea
pseudostratified columnar ciliated epithelium. There is only a single layer of epithelial cells, although it appears stratified- hence the 'pseudo'. In the ciliated epithelium is goblet cells that secrete mucus to trap inhaled particles. The cilia propel mucus and inhaled matter across the epithelial layer. Hyaline cartilage forms rings.
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Respiratory airways
conduct air between atmosphere and alveoli. Velocity of air decreases as it moves down the respiratory tree. Conducting portion of airway= trachea, bronchi, bronchioles, terminal bronchioles. Respiratory portion = alveoli
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Lungs and thoracic cavity:
Pressures on the lung and thoracic cavity create 'molecular glue'. Pleural space is a sac filled with fluid- its pressure is less than atmospheric due to the two opposing forces. The lung is stuck to the thoracic cavity, so when it expands, so do the lungs.
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Pressures in the lungs:
1. Intrapleural pressure: less than atmospheric. = pressure exerted outside the lungs in the thoracic cavity. Less than atmospheric ~ 756 mmHg. Pressure from alveoli and atmosphere hold this in place.
2. Intra-alveolar pressure: pressure in the alveoli ~760mmHg. Equilibrates with atmospheric pressure. Air inside pushes out.
3. Atmospheric pressure: ~760mmHg at sea level. Pushes inside
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Inspiration
Intercostal muscles and diaphragm expand the thoracic cavity (active process), this lowers the pressure in the cavity (Boyles law). Lungs will expand and air will come in passively, down its pressure gradient.
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Expiration
Passive as the inspiratory skeletal muscles stop contracting, the lungs will deflate, pulling the thoracic cavity with them. No energy is used as pressure will increase (Boyles law), resulting in air passively flowing out. If alveolar pressure is less than atmospheric, air will enter the lungs. If it is higher, air will exit.
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Boyles Law:
At any constant temperature, the pressure exerted by a gas varies inversely with the volume of a gas.
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Surface pressure on alveoli:
Alveoli resist being stretched as a layer of water molecules creates surface tension over the alveoli. The molecules want to be close, exerting an outward pressure attempting to reduce surface area and deflate the lungs. Diffusion of gas (oxygen) will not occur across dry membranes. Pulmonary surfactant positions itself between the water to reduce surface tension. Type I alveolar cells make up alveolar wall while type II alveolar cells secrete the surfactant molecules.
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Function of pulmonary surfactant:
1. Reduces stiffness of lungs
2. Reduces effort during inspiration
3. Keeps lungs 'dry'- too much liquid means that gases will have further to travel and gas exchange will be less efficient
4. Stabilises alveoli
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Dead space
where no gas exchange occurs. Is about 150ml in volume. The dead space will be the first air to be expired when we breathe out, along with 350ml of old air.
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Is alveolar air the same composition as inspired atmospheric air?
No. Alveolar Po2 is lower than atmospheric. When atmospheric air enters respiratory passages it becomes saturated with water. This has a partial pressure of 47 mmHg at body temp.
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During inspiration does Po2 in the alveoli increase?
Pressure does not increase in the alveoli during inspiration as only a small proportion of air is exchanged each breath. Oxygen continuously moves by passive diffusion down a partial pressure gradient from alveoli into the blood, not accumulating. Po2 remains constant. Po2 of the pulmonary blood is also constant as alveolar Po2 equilibrates with pulmonary blood.
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What changes pH?
free hydrogen ions
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3 defenses against changes in H+
1. chemical buffer systems- immediate response. First line of defence but cannot remove H+. Mix of two or more compounds in a reversible reaction that minimise pH changes. Carbonic acid and bicarbonate buffer pair is most essential, buffering changes in pH other than CO2 generated H2CO3. In normal conditions that ratio of bicarbonate to CO2 is 20:1. New H+ is added to plasma from any source other than CO2, driving reaction left. Any extra H will bind with HCO3. When H+ in plasma falls for reason other than a change in CO2 the reaction moves right. Dissolved CO2 and H2O will make H2CO3 which will generate more H+
2. respiratory control of pH- responds in minutes, eliminates H+ from a non CO2 source (For example lactic acid.) Controls rate of CO2 removal from plasma. Pulmonary ventilation can be altered to change the excretion of H+ generated CO2. Respiratory activity is governed by H+ concentration in arterial blood. If H+ increases, acidosis occurs, driving the equation left. Breathing rate increases to expire CO2 and remove H+. Peripheral chemoreceptors increase ventilation in response to more H+ in arterial blood. Central chemoreceptors increase ventilation in response to more PCO2 and brain ECF H+ concentration
3. renal mechanism of pH control- hours for a response. Can eliminate H+ from anywhere, for every H+ secreted a bicarbonate ion is added to the plasma where it can bind another H+. Kidneys control H+ and HCO3 concentrations and are the most potent regulation mechanism. Also control ammonia secretion
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Type A and B cells
Type A intercalated tubular cells are involved in hydrogen secretion. Type b cells are involved in bicarbonate ion secretion.
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Acidosis
In acidosis, secretion is increased causing more excretion of H+. All filtered HCO3- will be reabsorbed and new HCO3 will be added. Urine becomes acidic and plasma becomes alkaline.
Respiratory acidosis- Ratio of HCO3/CO2 falls below 20:1 from an increase in CO2 = acidosis.
Metabolic acidosis - HCO3-. ratio is less than 20:1 from a drop in HCO3. Excreted by diahorea
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Alkalosis
In alkalosis, secretion decreases leading to decreased excretion of H+ and HCO3- will not be reabsorbed completely. The urine will be alkaline to get rid of the excess HCO3 and the plasma will be acidic.
Respiratory alkalosis- CO2. ratio is greater than 20:1 from a decrease in CO2
Metabolic alkalosis - HCO3-. ratio is greater than 20:1 from an increase in HCO3. Vomit removes H+ from the body.
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Why can't the respiratory system fully compensate for imbalances in (H+)?
When there is a deviation in pH, peripheral chemoreceptors increase ventilation in response to more H+ in arterial blood. Centra chemoreceptors increase ventilation in response to more CO2. Both work at odds.
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Kidneys in regulating acid base
Most potent acid-base regulatory mechanism and can remove H+ from anywhere. Can conserve and eliminate HCO3. For each H+ excreted a new HCO3 is added to the plasma. Type A tubular cells secrete H ions that bind to filtered bicarbonate in the tubular lumen and make H2CO3. Type B cells secrete HCO3 into tubular lumen.
