Questions Flashcards
1
Q
What are the three foundations of biology?
A
Evolution through natural selection, unity of biochemical processes, and cell biology.
2
Q
What features are unique to prokaryotes?
A
Always microscopic Always unicellular No nucleus One circular chromosome Bacteria have no histones Bacteria have a peptidoglycan cell wall Smaller Ribosomes
3
Q
What features are unique to eukaryotes?
A
A division of labour in the cytoplasm
Nucleus and histones on DNA
An endomembrane system
A cytoskeleton
4
Q
What are the major functions of intracellular membranes?
A
Provide a surface for biochemical reactions
Establish a number of compartments to prevent mixing
Provide transport of materials within cell or out of cell
5
Q
What are the major elements of the cytoskeleton and their functions?
A
- Actin filaments interact with myosin motors. They contribute to muscle contractions and cytoplasmic streaming
- Microtubules interact with kinesin or dynein motors. Can form protofilaments that form flagellum (moved by dynein) or transport system for kinesin to carry molecules.
- Intermediate filaments are predominantly static
6
Q
What are the various ways molecules can cross membranes?
A
- Diffusion
- Osmosis - special case of diffusion, facilitated by aquaporins
- facilitated diffusion is diffusion facilitated by transport proteins (carrier or channel)
- Active transport (often coupled transport)
- Phagocytosis/Pinocytosis
7
Q
What are some of the ways an enzyme can reduce the EA of a reaction?
A
- Enzyme can help substrate reach activation energy
- Enzyme brings pieces together in the right orientation
- Enzyme strains the substrate
- Enzyme adds charges to substrate
8
Q
What is the role of ATP in energy harvesting/expending reactions
A
Energy released from an exergonic used to phosphorylate ADP to ATP, which is then dephosphorylated to drive an endergonic reaction.
9
Q
What are the key differences between cellular respiration and fermentation?
A
Cellular Respiration: - complete oxidation - aerobic - waste products: water and CO2 - Net energy trapped: 32 ATP Fermentation: - Incomplete oxidation - Anaerobic - waste products: organic compound and CO2 - Net energy trapped: 2 ATP
10
Q
What are the overall products of Aerobic Respiration?
A
Each Glucose yields 6 CO2, 10 NADH + H+, 2 FADH, 4 ATP
11
Q
What is the function of the Electron Transport Chain?
A
Electrons given up from reduced NADH are passed along the chain and used to reduce Oxygen, which then reacts with 2 H+ to form water. The proteins of the chain take some energy from the spin of the electron to pump protons from the mitochondrial matrix to the inner membrane space and create an electrical gradient. This gradient is harvested by ATP synthase which allows the protons back through and uses that energy to phosphorylate ATP
12
Q
What is the structure of ATP synthase?
A
ATP synthase is partially in and out of the inner mitochondrial membrane and has a rotating shaft. The protons cause the shaft to rotate while diffusing down, this powers the ‘forge’
ADP comes in with a phosphate and is given a whack, which initiates a covalent bond and creates ATP
13
Q
What is the evidence for the theory of endosymbiosis with mitochondria and chloroplasts?
A
- appear morphologically similar to bacteria
- surrounded by an outer membrane similar to the cell membrane while inner membrane invaginates to form lamellae or cristae. Derive from Gram negative bacteria
- semi autonomous, own genome (circular chromosome and small ribosomes)
- own machinery for synthesising proteins
- metabolism like existing prokaryotic organisms (cyanobacteria and purple bacteria)
- some chloroplasts still have a peptidoglycan cell wall between membranes
14
Q
What happens during interphase?
A
G1: each chromosome is a single, unreplicated DNA molecule with associated proteins. To move to the next stage, a checkpoint must be passed (DNA damage)
S: DNA replication. Each chromosome is duplicated to become two sister chromatids that remain joined until meiosis. The cell checks for incomplete replication or DNA damage
G2: The cell makes preparations for mitosis, such as synthesising and assembling structures. Checkpoint for DNA damage.
15
Q
What happens during Prophase?
A
The chromosome continues to coil and super coil, making it more and more compact and condensing into visible chromosomes. The chromosomes consist of identical, paired sister chromatids formed in S phase. The centrosomes start to develop the spindle and move to opposite poles.
16
Q
What happens during Prometaphase?
A
The nuclear envelope breaks down. Kinetechore microtubules appear and connect the kinetochores with the centromeres.
17
Q
What happens during Metaphase?
A
The centromeres become aligned in a plane at the cells equator. The cell checks that all kinetochores are attached.
18
Q
What happens during Anaphase?
A
The paired sister chromatids separate, and the new daughter chromosomes begin to move toward the poles.
19
Q
What happens in Telophase?
A
The spindle breaks down, the separated chromosomes reach the poles, nucleoli and nuclear envelopes reform and the cell divides by cytokinesis.
20
Q
How is cell division regulated?
A
Regulation and checkpoints rely on activity of cyclin-dependent kinases, which need to be activated by binding to a cyclin. Different combinations exist for various checkpoints, different cyclins are produced at different points in the cycle and can be inhibited if there is damage.
21
Q
What is different in Meiosis to Mitosis?
A
Meiosis I - homologs pair and exchange genetic material, separation in anaphase I does not separate chromatids, only homologous pairs
Meiosis II - mostly like mitosis but with no DNA replication, results in 4 genetically distinct daughter cells.
22
Q
Where might you find squamous cells?
A
Epithelial tissue cell type. Squamous cells are thin, and are typically found in layers (stratified). They are found in the skin.
23
Q
Where might you find columnar cells?
A
Epithelial tissue cell type. Columnar cells are tightly packed and have tight junctions. They can have cilia and are often polarised. They are often found in tubules.
24
Q
Where might you find cuboidal cells?
A
Epithelial tissue cell type. Cuboidal cells are tightly packed with tight junctions. These can also be found in tubules or in glands, or lining organs like the ovary.
25
What makes up cartilage?
Cartilage is rich in collagen and elastin, which makes cartilage firm and flexible.
26
What makes up bone?
Collagen fibres are hardened by calcium phosphate to provide a strong, rigid connective tissue.
27
What makes up adipose tissue?
Adipose cells form loose connective tissues that provides a barrier to heat loss.
28
What actions can the body take to reduce body temperature?
Evaporation, blood flow to skin, decreased metabolism.
29
What actions can the body take to increase body temperature?
Reduce blood flow to skin, increase metabolic rate.
30
What is the basic outline of a signal transduction pathway?
A signalling molecule binds to a receptor, causing a conformational change that may expose an active site. The receptor protein then conveys the message to the cell. This may be done by activating proteins or initiating a cascade of reactions. This will cause a response in the cell which could be short term (e.g. increase in enzyme activity), or long term (e.g. altered DNA transcription).
31
What determines the location of a signal's receptor?
The ability of the signal molecule to cross the phospholipid membrane.
E.g. cortisol has an intracellular receptor as it is a steroid, and is thus lipid soluble.
Thyroxine and Oestrogen receptors are found in the nucleus.
Acetylcholine is not lipid soluble and so has a membrane bound receptor.
32
Explain the action of a Gated Ion Channel Receptor.
This is direct transduction.
Binding of a signal causes a conformational change in the receptor such that the channel in the protein is open and ions can enter.
E.g. Acetylcholine binds to Sodium channels and allows them to enter, which may lead to contraction or an action potential.
33
Explain the action of a Protein Kinase Receptor.
This is indirect transduction via a second messenger.
The alpha subunit binds the signal, which causes the beta-subunit to change shape. This in turn activates the receptor's protein kinase domain in the cytoplasm, which phosphorylates the response substrate, leading to a cellular response.
E.g. Insulin receptors.
34
Explain the action of a G-Protein linked receptor.
When a signal binds to the receptor, a conformational change occurs which makes it possible for the G-protein to interact with the receptor, which phosphorylates GDP to GTP and activates the G-Protein. The G-protein subunit containing GTP is now able to move through the membrane and bind to an effector molecule, which initiates a cascade of reactions leading to a cellular response. The GTP is hydrolysed back to GDP.
E.g. Epinephrine binding to an epinephrine receptor leads to activation of Adenylyl Cyclase, which causes a cascade of reactions leading to increased glucose release and the prevention of glycogen production from glucose.
35
What are the characteristics of peptide/protein hormones?
Major group of hormones
Water soluble so are easily transported in the blood.
Not membrane soluble - receptors in membrane.
Packaged within vesicles in cells and secreted by exocytosis.
E.g. insulin.
36
What are the characteristics of steroid hormones?
Synthesised from steroid cholesterol
Lipid soluble so can pass through cell-membranes - internal receptors.
Diffuse out of cells and are bound to carrier molecules in the blood.
E.g. testosterone.
37
What are the characteristics of Amine proteins?
Mostly synthesised from tyrosine
can be water or lipid soluble so mode of action differs
E.g. Epinephrine, Thyroxine.
38
What hormones are secreted by the Anterior Pituitary and what do they do?
- Thyrotropin Stimulating Hormone (TSH) - targets thyroid gland and causes Thyroxine release.
- ACTH - targets adrenal gland and causes Cortisol release
- Follicle Stimulating Hormone (FSH) - stimulates oocyte maturation and release in ovary, supports function of sertoli cells in the testis
- Growth Hormone (GH) - stimulates protein synthesis and growth in most cells, stimulates milk production in breast cells.
39
What hormones are secreted by the Posterior Pituitary and what do they do?
```
Releases Neurohormones that are secreted into blood by neurons that originate in the hypothalamus
Oxytocin - stimulates contractions in uterus.
Antidiuretic Hormone (ADH) - regulates water uptake in kidneys.
```
40
What is the structure and function of the Adrenal Gland?
Has an outer cortex and an inner medulla.
The outer cortex secretes cortisol and aldosterone.
The inner medulla secretes epinephrine and norepinephrine.
41
What is the Fight or Flight Response?
Release of Epinephrine and Norepinephrine in response to stressful situations. Rapid release as the adrenal medulla is controlled by the nervous system.
Targets the circulatory system, muscles, liver and fat cells.
Causes heart to beat faster, blood pressure increase, blood flow diverted to muscles, liver cells break down glycogen and secrete glucose, fat cells release fatty acids.
42
How does hormone release in the Anterior pituitary work?
Controlled by the hypothalamus.
Neurohormones in the hypothalamus have terminals on blood vessels in the stalk, these neurons secrete releasing neurohormones that travel via the portal blood vessels to the anterior pituitary where they act on cells to stimulate the release of hormones into the blood. Thus the anterior pituitary is an endocrine gland.
43
How are hormones from the pituitary regulated?
The External or Internal signal can stimulate or inhibit the hypothalamus.
Hypothalamic neurons secrete releasing hormones that stimulate anterior pituitary cells to release tropic hormones. These tropic hormones inhibit the hypothalamus, but also stimulate an endocrine gland to produce a hormone.
This hormone causes a cell response, but also negatively feeds back to they hypothalamus and to the pituitary.
44
What is thyroxine?
A lipid soluble hormone secreted by the thyroid that binds to nuclear receptors in most body cells and activates transcription of enzymes involved in metabolic pathways. This causes an increase in metabolic rate, often in response to temperature changes.
Thyroxine is crucial for development and growth.
45
How is thyroxine synthesised and secreted?
- A follicle cell in the thyroid takes up iodine from the blood.
- The cell synthesises thyroglobulin from tyrosine.
- Thyroglobulin is secreted into the follicle lumen and iodinated.
- Iodinated thyroglobulin is taken up by the follicle cell by endocytosis.
- Lysozymes break up thyroglobulin into T3 and T4
- T3 and T4 are secreted into the blood.
This process is stimulated by Thyroid Stimulating Hormone (TSH), which is regulated in the same was as other anterior pituitary tropic hormones via negative feedback.
46
What is hyperthyroidism?
A disease of the thyroid gland characterised by very high levels of thyroxine. Autoimmune (Grave's Disease), an antibody binds to the TSH receptor in follicle cells of thyroid, causing high levels of Thyroxine, but low levels of TSH - negative feedback ineffectual.
Symptoms: High MR, feeling hot, enlarged thyroid gland, weight loss.
47
What is hypothyroidism?
A disease of the thyroid gland characterised by very low levels of Thyroxine.
Can be autoimmune (Hashimoto's Disease) or be caused by low dietary iodine, meaning the follicle cells fail to make thyroxine.
No negative feedback of TSH, so thyroid continues to make thyroglobulin, but poorly iodinated.
Symptoms: enlarged thyroid, low cell metabolism, intolerance to cold, physical and mental lethargy.
48
What is the autonomic nervous system?
An important part of the peripheral nervous system controlling involuntary activity.
Parasympathetic = rest and digest
Sympathetic = Fight or flight
49
How are action potentials communicated between cells?
When the action potential is received by the axon terminal, it stimulates the influx of Ca2+, which stimulates the release of vesicles filled with neurotransmitters into the synaptic cleft by endocytosis.
These neurotransmitters bind to receptors on the postsynaptic cell and initiate a response
50
What is the Limbic System?
Portion of the central nervous system responsible for instincts, long term memory formation and physiological drives such as hunger, thirst, pleasure and pain.
Amygdala: fear and fear memory
Hippocampus: transfers short term memories to long term memories.
51
What parts of the brain are responsible for language?
Language abilities usually localised to the left hemisphere.
Broca's area (Frontal lobe) is essential for speech, movements required to produce speech.
- damage will result in loss of ability to produce language, broken speech, but patient is aware and can understand language
Wernicke's are (Parietal and Temporal Lobe) is essential for understanding speech and use of correct words, more sensory than motor aspects, commands to speak formed here
- damage will result in inability to understand language, can't choose the right words or express thoughts, patient is not aware, can speak clearly but doesn't make sense.
Normal language depends on the flow of information among various areas of the brain.
52
In what ways does sleep help learning and memory?
Helps you to focus well during waking hours and forms neural connections to store newly acquired information while you sleep.
53
What is the typical timeline of an immune response?
0-4 hours: infection recognised by phagocytes and soluble components of the innate immune system, reliance on barriers (1st line)
4-96 hours: Recruitment of effector cells of the innate response (induced response, 2nd line)
96+ hours: Transport of antigen to lymphoid organs for recognition by T and B cells and proliferation of these cells (3rd line)
Removal of infectious agent
54
What are the characteristics of the innate immune response?
Non specific
Typically very rapid
Involves recognising components that are common to many pathogens
1st line of defense mostly barrier based: skin, mucus, cilia, chemicals, acids etc
2nd line involves cells and other molecules: phagocytes, the complement, interferons, inflammation, fever, mast cells
55
What are the characteristics of the adaptive immune response?
Ability to distinguish between self and non self
Typically slow to develop and usually long lasting
Involves recognising components that are specific to each particular pathogen
Involves action of lymphocytes
Cellular and Hummoral responses.
Four key features: specificity, ability to distinguish self from non-self, diversity and immunological memory
56
What is the role of Macrophages in the immune system?
Macrophages are phagocytic and have function in both the innate and adaptive immune systems. Their role is to engulf and digest pathogens, cellular debris and infected cells.
Macrophages are often found stationed in areas where infection is likely to occur (special names)
- some like to circulate in blood and lymphatic vessels
- some can move through the blood vessels to the site of damage
- Phagocytes use defensins and other factors to kill pathogen after engulfing
57
What are the three phases of a defensive response?
Recognition: organism must discriminate between self and non-self
Activation: mobilisation of cells and molecules to fight invader
Effector: mobilised cells and molecules destroy invader.
58
How does inflammation occur?
Injury causes histamine release from mast cells, which are attracted to the area of injury. Histamine causes vessels to dilate and become leaky. Complement proteins move from blood to infected area and bind to and engulf pathogens. This attracts phagocytes/macrophages, which move from the blood to the infected area and bind and engulf pathogens.
Blood plasma also moves into infected area causing oedema.Platelets from blood release growth factors, which stimulates dermis cells to divide and heal the wound.
Pain is due to increased pressure of swelling and prostaglandins released from mast cells which increase the sensitivity of pain receptors
59
How does specificity work in the adaptive immune system?
The humoral immune response employs antibodies secreted by plasma cells to target antigens in body fluids - involves antibodies and B-cells
The cellular immune response employs T-cells to attack body cells that have been altered by viral infection or mutation or to target antigens that have invaded the body's cells - involves T-cells and T-cell receptor.
Each T-cell and each antibody is specific for a specific antigen determinant.
60
What is the structure of an antibody?
An antibody has four polypeptide chains (2 light, 2 heavy) and is bivalent, meaning it has two identical binding sites for antigens.
Each of the four polypeptide chains has a variable and a constant region - each variable region is specific for one antigen
Disulphide bonds hold the peptides together and the base of the heavy chain determines the class.
61
What is the structure of a T-cell receptor?
T-cell receptors are membrane bound glycoproteins. They have two polypeptide chains with different amino acid sequences (alpha and beta), each with a variable and constant region. The variable region of the two chains direct the specificity of the antigen binding site.
62
How does an antigen presenting cell work?
An antigen presenting cell, such as a macrophage, has membrane receptors for the constant region of the heavy chain region of antibodies bound to antigenic determinants on antigens. The binding of the antibodies to the macrophage receptor activates phagocytosis. The cell then breaks the antigen down into fragments and a class II MHC molecule binds the antigen fragment and carries it to the membrane, where it presents it to a T-helper cell.
63
How does diversity work in the adaptive immune system?
There are millions of possible specific antibodies and T-cell receptors as a result of the many possible DNA recombinations in the variable regions.
64
How does memory work in te adaptive immune system?
B-memory cells have membrane bound antibodies that bind pathogens, causing the complex to be endocytosed. this activates the memory. The immune system can now respond more quickly and powerfully if that pathogen invades again. Endocytosis of an antigen also triggers the proliferation of more lymphocytes specific for that antigen, generating a clone/colony of effector cells and memory cells.
65
How can pluripotent embryonic stem cell like cells be created from somatic cells?
Adding the Yamanaka factors (four genes) causes somatic cells to be reprogrammed into induced Pluripotent ES-like cells (iPS cells). These cells can now become any specialised somatic cell spontaneously, resulting in a mixture of cell types, or, if specific signal combinations are added, can be induced to become a particular cell type.
66
What relation does obesity have to fertility issues?
Obesity in females can lead to fertility issues such as anovulation, changes to the menstrual cycle and pregnancy complications. In males it can mean a longer time to conceive.
67
Why is digestion necessary?
Food must be subjected to physical and chemical changes for absorption. This involves physically breaking down food to smaller pieces to increase the surface area, and breaking down complex molecules to smaller monomers that can be absorbed.`
68
What happens in the oral cavity?
Physical breakdown (mastication) of ingested food via chewing. Enzymatic digestion by amylase, breaks starch/glycogen down to maltose.
69
How does the stomach digest food?
The stomach has a thick muscular wall that churns the food, breaking it up and mixing it with the gastric juices. The inner wall of the stomach is folded to increase surface area, creating gastric pits, which contain three types of secretory cells.
Chief cells secrete pepsinogen, which is the zymogen of the protease pepsin, which breaks protein down into amino acids and smaller peptides.
Parietal cells produce hydrochloric acid via a chloride bicarbonate exchange using co-transport across the membrane and secretes it into the gut lumen. The HCl cleaves pepsinogen and converts it to pepsin, which in turn activates other pepsinogen molecules.
The gastric mucosa epithelial cells secrete mucus, which protects the tissue from HCl and pepsin.
70
How are fats digested in the small intestine?
The liver produces bile, which emulsifies fats and forms micelles, preventing them from sticking together. Pancreatic lipase then hydrolyses the fats in micelles to produce fatty acids and monoglycerides.
These enter villi cells by diffusion and a resynthesised into triglycerides in the endoplasmic reticulum. These are then packaged with cholesterol and phospholipids in protein coated chylomicrons.
The chylomicrons are package into vesicles and leave the cell by exocytosis and enter the lymphatic system.
Excess fat is stored in adipose tissue.
71
What is the structure of the gut and how is it controlled?
There are two layers of smooth muscle outside the sub mucosa. The innermost cells constitute a circular muscle layer. These are oriented around the gut and constrict it. The outermost cells constitute the longitudinal muscle layer, and are oriented along the gut, shortening it. Both are controlled by the Enteric Nervous System, which is in constant communication with the Central Nervous System
72
How are carbohydrates absorbed in the small intestine?
Carbohydrates are absorbed as monosaccharides into the capillaries of villi. Glucose is taken up by active transport as it needs to be pumped against a concentration gradient. The blood vessels then drain into the hepatic portal vein, which carries blood to the liver, where the glucose is converted to glycogen and stored.
73
How are proteins absorbed in the small intestine?
Proteins are absorbed into capillaries as amino acids. These are then taken up directly by cells which are synthesising proteins. Excess amino acids are de-aminated by the liver, which uses nitrogen to form urea for excretion.
74
How are water, salts and alcohol absorbed?
These are able to be absorbed directly into underlying blood vessels irrespective of need. Any excess is excreted by the kidneys.
Alcohol is also absorbed directly through the stomach.
75
What controls digestive secretion?
Digestive secretion is controlled both by the endocrine and nervous system to ensure a sequential release of enzymes.
- salivation is under nervous control
- food entering the stomach stimulates the release of gastrin from the stomach mucosa, which causes the release of HCl and pepsin.
- presence of acid in the duodenum causes the release of secretin from intestinal mucosa into the blood, causes the pancreas to release HCO3- and gall bladder to release bile.
- presence of fats and proteins in chyme induces mucosa of small intestine to secrete cholecystokinin, which also stimulates the gall bladder to release bile, and together wiht secretin, act to slow the movements of the stomach, and slow the delivery of chyme to the small intestine
76
What are the advantages of a closed circulatory system?
- faster and more efficient delivery of fluid to tissues
- ability to control distribution of blood to specific tissues
- assists in delivery of larger molecules
- enabled the evolution of circulatory systems which kept oxygenated blood separate from deoxygenated blood.
77
What is the structure of a fish circulatory system?
- one atrium and one ventricle = one circulation
- specialisation of vessels (arteries and veins)
- blood pumped over gills to become oxygenated but leaves under very low pressure - limits efficiency of delivery in capillaries
(Air breathing fish have two circulations and a partially divided atrium and ventricle. The resistance of the two circuits can be altered as needed).
78
What is the structure of the amphibian circulatory system?
- three chambered hearts (two atriums - left receives oxygenated blood from lungs, right receives deoxygenated from body)
- single ventricle with a septum that directs blood movement and maintains ~90% separation of blood
- partial separation of pulmonary and systemic circuits allows different pressures
79
What is the structure of the reptilian circulatory system?
- three (or 4) chambered hearts
- two aorta: left takes oxygenated blood from the left ventricle to the body, right receives blood from both ventricles (mixed)
- don't always have to breathe - blood can bypass the lungs and flow directly to the systemic circuit via the right aorta
- direction of flow is controlled by resistance in the pulmonary circuit, which is lower when the animal is breathing
80
What is the structure of the avian and mammalian circulatory systems?
- four chambered hearts, with total separation of oxygenated and deoxygenated blood
- separate pulmonary and systemic circuits that can operate at different pressures - ensures systemic circuit always receives blood with higher oxygen content and gas exchange is maximised.
81
How is cardiac muscle specialised for its function?
Involuntary striated muscle with cross striations formed by alternating segments of thick myosin and thin actin filaments. Cardiomyocytes have one nucleus and branch to form a network.
Intercalated discs link adjoining cells and provide mechanical adhesion between cardiaomyocytes - cells pull together rather than apart.
Gap junctions allow rapid transmission of electrical signals, allowing for coordinated muscle contraction.
82
Describe a cardiac cycle.
During diastole, the atria contract and blood flows into the ventricles. Pressure in the left ventricle is low while aortic pressure falls. Then the AV valves close, creating the lub sound. During systole, the ventricles contract, pressure in the ventricles builds up until the aortic and pulmonary valves open. blood is pumped out of the ventricles and into the aorta and pulmonary artery, causing the pressure there to increase. The semilunar valves then close, creating the dub sound. Back in diastole, the ventricles relax and pressure falls back down after the end of systole. Pressure is now greater in the arteries
83
How are arteries specialised for their function?
Arteries must withstand high pressure - many collagen and elastin fibres in tunica adventitia and media (elastin) which strengthen the vessel wall
Aorta expands and contracts elastically, has elastin fibres that stretch during systole and store energy which is used to propel blood forwards in diastole.
Arteries are able to adjust their diameter and resistance to flow - have smooth muscle in the tunica media which contracts to cause vasoconstriction
Endothelial cells in tunica adventitia produce factors that cause vasodilation or vasoconstriction.
84
How are veins specialised for their function?
Vein walls are expandable, there are no thick muscle walls and not as much collagen in adventitia, thus they are able to store blood
Veins must be able to return blood to the heart under low pressure, they possess some smooth muscle which contracts, this is a thin layer, but the large blood volume means a small contraction moves a lot of blood.
Veins have one way valves to prevent backflow of blood (often due to gravity)
Contraction of skeletal muscles surrounding the veins helps in venous return
85
How are capillary beds specialised for their function?
Capillary beds provide a massive surface area due to sheer volume of capillaries which maximises material exchange
Capillaries are very narrow, causing blood flow to slow, and allowing for ease of exchange
Single layer of endothelial cells which improves diffusion and osmosis.
Have tiny holes (fenestrations) that allow water, some ions and very small proteins out.
86
How is fluid balance maintained in the capillaries?
Starling's forces are two a=opposing forces that maintain water balance in the capillaries.
Blood pressure tends to force water and small solutes out.
Osmotic pressure tends to draw water back in, due to large protein molecules that cannot leave capillaries.
Osmotic pressure remains the same along the capillaries, while blood pressure decreases.
As long as the blood pressure is greater than osmotic pressure, fluid will be forced out. At the venular end of the capillaries, the blood pressure has decreased below osmotic pressure so fluid is pulled back in
87
How does the heart control its own contractions?
Specialised cells in the Sinoatrial node spontaneously depolarise to generate an action potential which spreads through gap junctions in the atria and they contract together, but does not spread to the ventricles.
The action potentials in the atria stimulate the atrioventricular node to send action potentials to the ventricles via the Bundle of His, a neural pathway which divides into left and right bundle branches that run down the septum to the apex of the heart and then divide into the Purkinje Fibres that spread the action potential throughout the ventricles. Thus a contraction spreads rapidly and evenly throughout the ventricles from the bottom up.
88
How is the circulatory system regulated?
The circulatory system is regulated by both the nervous system and the endocrine system in response to changes in blood pressure and increased demand for oxygen.
89
How does vasoconstriction occur?
Norepeniphrine acts through a1-adrenoreceptors, Angiotensin II acts through AT1 receptors, Endothelin acts through ETA receptors.
Ligand binding to these receptors in the vascular smooth muscles activates phosphlipase C (PL-C) causing formation of inositol triphosphate (IP3) which then stimulates the sarcoplasmic reticulum to release Calcium.
Ca2+ acts with actin and myosin to cause contraction of smooth muscle.
90
How does vasodilation occur?
A vasodilater such as Bradykinin binds to a receptor on endothelial cells. Three responses:
An increase in calcium causes release of potassium across membrane through couple transport, where it then moves into smooth muscle cells, causing hyperpolarisation and thus relaxation.
Nitric Oxide is formed and activates Guanylate Cyclase in the membrane of the smooth muscle cells, which hydrolyses GTP to cGMP, causing hyperpolarisation through a cascade and relaxation.
Prostacycline is produced, which activates Adenylate Cyclase on the membrane oc smooth muscle cells, which hydrolyses ATP to cAMP, which through a cascade causes hyperpolarisation.
91
How does the Autonomic Nervous System control heart rate?
Extrinsic factors alter heart rate by acting on the pacemaker cells in the Sinoatrial Node.
To increase heart rate, norepinephrine is released from sympathetic neurons and from the adrenal medulla (with epinephrine) These act on the adrenoreceptors in the SAN causing more Na+ and Ca2+ channels to open in the pacemaker cells, increasing the rate of depolarisation.
To decrease heart rate, acetylcholine is released from parasympathetic neurons and acts on muscarinic receptors in the SAN to open more K+ channels, which hyperpolarise the cell and increase the time for depolarisation.
92
What are the characteristics of an exchange site in the respiratory system?
Large Surface Area
Small diffusion distance between respiratory medium and the blood or between the blood and tissues
Highly vascularised
93
What are the characteristics of different types of ventilation systems?
Ventilation systems keep a constant supply of medium moving across the respiratory exchange site, improving the rate of gas exchange and ensuring that fresh supplies of oxygen rich medium are supplied to the exchange site.
A mouth and operculum allow unidirectional flow of water across gills
A buccal cavity allows for a tidal flow of air
Air sacs give a system for two cycles of inhalation and exhalation (unidirectional).
94
How does the cooperativity displayed in Haemoglobin help in oxygen transportation?
In oxygen low environments, the affinity haemoglobin has for oxygen is lower, so it releases oxygen in areas where it is needed, and this release decreases the affinity haemoglobin has for the rest of the oxygen bound to it, allowing it to leave easier. In oxygen rich environments such as the lungs, the affinity of haemoglobin for oxygen is high, and when one molecule binds, this affinity increases, increasing the speed at which oxygen binds.
Thus the cooperativity of Haemoglobin ensures for a more efficient pick up and delivery of oxygen.
95
What is BPG and what does it do?
BPG (2,3-bisphosphogyceric acid) is a mammalian glycolysis metabolite found in red blood cells.
It reversibly combines with partly deoxygenated Hb and lowers its affinity for oxygen, thus causing it to release remaining oxygen.
BPG helps Hb to deliver more oxygen to tissues at high altitudes or with increased exercise.
96
How does myoglobin's high affinity for oxygen assist in it's function?
Myoglobin provides an oxygen reserve in the muscles, and it's high affinity for oxygen means that it releases oxygen only at very low partial pressures, so this reserve is not used up quickly.
97
How is Carbon Dioxide transported in the blood.
Three ways:
- 10% dissolved in plasma
- 30% reversibly bound to haemoglobin: carbaminohaemoglobin
- 60% as bicarbonate - converting CO2 to HCO3- reduces PCO2 in the blood, ensuring more carbon dioxide diffused out of tissues.
98
How do red blood cells convert carbon dioxide to bicarbonate?
Carbon dioxide enters and with water is reacted by carbonic anhydrase to form H2CO3, and then the bicarbonate ion. There is a chloride/bicarbonate exchange where chloride ions move in to red blood cells to balance the charge when HCO3- is removed.
H+ buffering is provided by haemoglobin.
The reverse reaction occurs in the lungs.
99
How do gills work?
Gills are an invaginated extension of the body surface that are highly folded to increase surface area and are protected by an operculum.
A pumping mechanism moves water over the gills and an internal circulatory system distributes blood throughout the gills and body.
The lamellae increase surface area for gas exchange and reduce the diffusion path length between water and blood.
A unidirectional flow of water through the gills is achieved by sequential opening and closing of the mouth and operculum and a small pressure differential between the buccal and opercular cavities.
100
What is the purpose of mucus in the lungs?
Many epithelial cells (goblet cells) lining the airways produce a sticky mucus that captures inhaled dirt and microorganisms. Other cells lining the airways have cilia whose beating continually sweeps the mucus, which its trapped debris, up towards the pharynx.
This is known as the mucus escalator. Many respiratory problems are associated with a malfunctioning mucus escalator.
Smoking immobilises the cilia for hours - mucus cannot be cleared
Cystic Fibrosis - unusually thick and dry mucus obstructs airway and cilia function (result of a nonfunctional chloride channel - water cannot leave cell into mucus).
101
What is the purpose of lung surfactant?
There is a layer of water on lung tissue so that gases can dissolve. The high surface tension of water means that the water molecules are attracted to each other and have the potential to cause the alveoli to collapse.
Lung surfactant is a phospholipoproten secreted by some alveolar cells that breaks up this surface tension and causes layers of water to push towards the alveolar wall, meaning less force is required to inflate the lungs.
102
How does the diaphragm control breathing?
During inhalation, the diaphragm contracts and pulls down on the thoracic cavity and pleural membranes, which pull on the lungs. This increases the volume of the lungs, decreasing the pressure, causing air to be sucked in.
During exhalation, the diaphragm relaxes and the elastic lung tissues pull it back up, pushing air out of the airways.
103
What are the pleural membranes and pleural cavity?
The pleural membranes line the pleural cavity and cover each lung.
Parietal pleural connective tissue lines the cavity, visceral pleural connective tissue lines the lungs, and the fluid between them keeps them essentially stuck together.
104
How can the intercostal muscles augment breathing?
Inhalation is aided by the contraction of external intercostals, which push the ribs out and increase the thoracic volume.
Exhalation is aided by the contraction of the internal intercostals, which pull the ribs in and decrease thoracic volume.
105
How is respiration regulated?
Respiration is normally involuntary but can be voluntary.
Sensory inputs from chemoreceptors in the medulla, aorta and carotids are sent to the respiratory centre in the brainstem (pons and medulla), which determines the depth, amplitude and frequency of breathing. The pons sets the rhythm and modifies medullary pattern.
The phrenic nerve controls contraction and lowering of diaphragm wile the efferent nerves activate the intercostals.
Breathing rate is more sensitive to increased CO2. An increase in blood PCO2 will cause an increase in breathing rate to match metabolic demand.
106
In what ways do various animals overcome the problems of hypoxia?
- hyperventilation due to activation of chemoreceptors in aortic and carotid bodies to maintain sufficient oxygen delivery
- increase in gill ventilation due to stimulation of chemoreceptors in the gills.
- reduce in energy expenditure and use of anaerobic metabolic pathways
- increase in BPG
107
What are the main functions of excretory organs?
- maintain osmotic concentrations
- maintain body fluid volume
- maintain proper ion concentrations
- remove metabolic end products
- remove foreign substances
This is done by excreting water and solutes that are in excess and conserving water and solutes that are in short supply.
108
What are the three nitrogen excretory products?
Ammonotelic animals excrete nitrogen as ammonia (NH3) which is toxic and must be removed quickly. Ammonotelic animals are aquatic, water is readily available to remove ammonia (very soluble)
Uricotelic animals excrete nitrogen as uric acid. (Land reptiles, birds and insects)
Ureotelic animals excrete nitrogen as urea, which is synthesised from CO2, water, asparate and ammonia in a metabolic pathway called the urea cycle, which occurs in the liver and requires energy. (mammals, amphibians and cartilaginous fish)
Uric acid and urea need less water to remove and thus conserve water.
109
What are the osmoregulatory struggles faced by animals in different environments?
Marine animals have to conserve water and excrete excess salts.
Freshwater animals have to excrete excess water and conserve salts
Terrestrial animals must conserve water and salts.
All have to excrete nitrogenous waste.
110
What are osmoconformers?
Osmoconformers don't regulate the osmolarity of their body fluids, but equilibrate them to external osmolarity. They are only found in the sea, and constitute most marine invertebrates.
111
What are osmoregulators and how are they adapted to maintain osmolarity?
Osmoregulators survive in varied environmental osmolarities by maintaining the osmolarity of their body fluids.
The internal environment is hypoosmotic to the external environment
They drink seawater to replace the water lost to the environment
Produce very little urine
Eliminate the salts ingested from salt water (much through gills)
Gills act as excretory organs, chloride cells actively transport salts out.
112
How are desert animals adapted to conserve water?
Behavioural - avoidance of daytime heat
Aestivation (like hibernation) low metabolism so low water turnover
Thick keratinised cuticle with a high lipid content (reptiles)
Efficient kidneys and excrete highly concentrated urine (long loops of Henle) (birds and mammals)
113
What constitutes a nephron?
The nephron is the functional unit of the vertebrate kidney and consists of:
- a glomerulus, in which blood is filtered across the walls of a mesh of capillaries
- a renal tubule, which process the filtrate into urine (loop of henle)
114
How is blood filtered in the Glomerulus?
The glomerulus is a dense ball of capillaries which filters blood plasma to produce renal filtrate, which lacks in cells, proteins and other large molecules.
The Bowman's Capsule receives the renal filtrate, which is mainly water and smaller molecules such as glucose, amino acids and ions.
The rate of filtration is high in the glomerulus due to:
- high capillary blood pressure
- high permeability of glomerular capillaries and their podocytes (wrap around capillaries and leave slits between them - stop RBCs and large proteins getting through)
115
What happens in the proximal convoluted tubule and how is the PCT specialised for this?
PCT cells are cuboidal with increased surface area due to microvilli. They possess large numbers of mitochondria and are highly metabolically active. PCT cells actively transport Na+, glucose and amino acids out of the filtrate and back into tissue fluid. This causes water to follow by osmosis, which is regulated by AQP1.
Water and solutes in the tissue fluid are then taken up by the vasa recta
116
What's up with Aqp1-/- mice?
They cannot concentrate their urine because there is no movement of water form the renal filtrate in the PCT (AQP1 not there!)
117
What is the purpose of the loop of Henle?
The loop of Henle produces a concentration gradient in the surrounding medullary tissue.
This causes the urine to become more concentrated; hyperosmotic to the blood later on.
The loop of henle is found in birds and mammals, where it is important for water conservation.
The filtrate concentration changes along the renal tubule.
118
What happens in the thin descending limb of the loop of henle and how is it specialised for this function?
The thin descending limb contains lots of aquaporins and is highly permeable to water but not to Na+ and Cl-
The surrounding interstitial fluid is more concentrated, so water exits by osmosis through the aquaporins, and therefore the renal fluid in the descending limb becomes more concentrated.
119
What happens in the thick ascending limb of the loop of henle and how is it specialised for this function?
The thick ascending limb actively pumps Cl- out of the filtrate and into the interstitial fluid. Na+ ions follow passively to balance the electrochemical gradient.
This part of the tubule is impermeable to water so water does not follow.
This reabsorption raises the solute concentration in the surrounding interstitial fluid of the medulla.
120
What happens in the distal convoluted tubule and how is it specialised for this function?
In the distal convoluted tubule:
- renal fluid is less concentrated then the interstitial as the solutes have left
- reabsorption of salts, amino acids, etc. occurs via active transport depending on the body's needs
- some water moves out by osmosis.
- renal fluid becomes isosmotic with interstitial fluid.
121
What happens in the collecting duct and how is it specialised for this function?
As the renal fluid moves down the collecting duct, it becomes highly concentrated as water is drawn out due to the high concentration gradient in the interstitial fluid of the medulla.
The collecting duct is permeable to water due to a high presence of AQP2 but not to ions.
Urea is now the major solute in the renal fluid, as most other solutes have been removed.
122
How is water reabsorption in the kidneys regulated?
A rise in blood osmolarity is detected by osmoreceptors, which stimulate ADH (vasopressin) release. This increases water permeability of the collecting duct and distal tubule as ADH stimulates the expression of AQP2. Thus more water is reabsorbed and blood osmolarity decreases.
Increase in water reabsorption leads to increase in blood pressure, which is detected by baroreceptors in the aorta and carotid arteries, which inhibit the release of ADH, causing less water to be reabsorbed, and blood pressure to decrease.
123
What are brattleboro rats?
Have a mutation in the vasopressin (ADH) gene. Kidneys don't return water to the blood, so they must excrete it.
Rat constantly urinates and must drink a lot to replace this lost water.
124
What is the Renin-Angiotensin-Aldosterone System (RAAS) and how does it work?
An important auto-regulatory mechanism to maintain blood volume and blood pressure.
When blood pressure falls, juxtaglomerular cells detect this and secrete Renin.
Renin cleaves angiotensinogen to angiotensin I.
AngI is then converted to AngII by Angiotensin converting enzyme (ACE).
AngII cause constriction of peripheral blood vessels, release of aldosterone (which enhances Na+ reabsorption and hence water reabsorption in the distal convoluted tubule and collecting duct), and stimulation of thirst and drinking.
Vasoconstriction of the efferent vessel of the nephron increases blood pressure and negatively feeds back to the juxtaglomerular cells.
125
What are the main features of animals compared to members of the other kingdoms?
Multicellularity (cell junctions and extracellular matrix)
Heterotrophy
Internal Digestion
126
What are the four main features of mammals?
Sweat Glands
Mammary Glands
Hair
4 chambered heart
127
What are the advantages and disadvantages of asexual reproduction?
Advantages
- not as energy expensive
- able to reproduce without a partner - ensures genes are passed on to the next generation
Disadvantages
- does not generate genetic diversity - no adaptation, harder to evade pathogens
128
What are the advantages and disadvantages of sexual reproduction?
Advantages:
- Generates genetic diversity, enabling adaption and evasion of pathogens
Disadvantages:
- Energy expensive and complex
129
How are sperm adapted for their function?
Consist of only a head with a nucleus, body with mitochondria and flagellum for movement.
Head has an acrosome coating which contains enzymes to help penetrate the ovum.
Mitochondria provide energy required to swim.
130
What are the steps of spermatogenesis?
The diploid mail germ cell (part of the stem cell population which continuously proliferates to renew itself) divides by mitosis to produce diploid spermatogonium, which then divide mitotically to produce the primary spermatocyte. The first meiotic division produces two haploid secondary spermatocytes, which then divide again in meiosis 2 to produce four haploid spermatids joined by cytoplasmic bridges. These then differentiate into spermatozoa.
All of this occurs in the seminiferous tubules.
131
What are the steps of oogenesis?
Oogonia proliferate through mitosis before a female is born. When they develop into primary oocytes they immediately enter prophase I of meiosis and stay there for many years (The Geminal Vesicle Stage) until the female reaches puberty.
About once a month between puberty and menopause, 6-12 primary oocytes begin to mature.
The developing oocyte is nourished by surrounding follicular cells, which also produce eostrogen.
After one week, usually only 1 primary oocyte continues to develop. A meiotic division just before ovulation creates the haploid secondary oocyte and the first polar body.
At ovulation, the follicle ruptures, releasing the egg, which is surrounded by the cumulus oophorus.
Meiosis is only completed upon fertilisation, when the second polar body is pushed out.
132
What are the different types of follicles?
- Primordial Follicle - present in the ovary from birth, located in the stroma of the ovary cortex beneath the tunica albuginea. The primordial follicle is the oocyte and the surrounding follicular cells.
- Primordial Germ Cell - the oocyte present in the primordial follicle from birth
- Primary follicle - single layer of follicle cells, presence of zona pellucida
- secondary follicle - two or more layers of follicle cells
- Antral (Graafian) Follicle - Early or late - presence of cavity and multiple layers of cells
133
What are the barriers to sperm around the egg?
The sperm must bypass the cumulus oophorus in order to reach the egg. In mammals, a species-specific protein in the zona pellucida binds a sperm and triggers the acrosomal reaction.
134
What are the stages of fertilisation?
- Sperm swim through the cumulus oophorus
- sperm bind to proteins of the zona pellucida with species specific binding, this stimulates acrosomal reaction: enzymes released that lyse a hole through the zona pellucida
- Sperm membrane fuses with Egg membrane - triggers egg activation, egg completes meiosis
- centriole and sperm nucleus enter cytoplasm
- cortical granule reaction blocks polyspermy
135
What are the components of semen?
Semen consists of sperm suspended in a fluid that nourishes them and facilitates fertilisation.
- 5% sperm
- 30% prostate gland fluid - alkaline to neutralise acidic pH of vagina
- mucus and fibrinogen, as well as a clotting enzyme to act on fibrinogen and convert semen into coagulum
- fructose
136
How does the hypothalamus regulate male reproductive organs?
The Hypothalamus produced gonadotropin-releasing hormone (GnRH) which stimulates the anterior pituitary to secrete Leuteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH).
LH stimulates the Leydig Cells (between the sertoli cells in the testes) to produce testosterone, which stimulates development of secondary sexual characteristics and stimulates sertoli cells to spermatogenesis. A high level of circulating testosterone inhibits GnRH and LH production.
FSH stimulates the sertoli cells to promote spermatogenesis and to produce the hormone inhibin, which inhibits FSH production.
At puberty, there is an increase in GnRH and the sensitivity of the hypothalamus to the negative feedback of testosterone declines.
137
How are female reproductive hormones produced?
Both oestrodiol and progesterone are produced in the Follicle from cholesterol.
The cells of the theca produce testosterone from cholesterol in the presence of LH.
The cells of the granulosa then produce oestradiol from testosterone in the presence of FSH, as well as progesterone from cholesterol.
138
How do hormones control the female reproductive cycle?
During the follicular phase and menstruatuion (days 1-14), LH and FSH released by the anterior pituitary stimulate the growth of follicles in the ovaries, which begin to produce oestrogen. An LH spike at day 14 triggers ovulation and corresponds with a surge in oestrogen and FSH. After ovulation, the corpus luteum begins to produce progesterone, which maintains the endometrium to receive the embryo.
139
What are the stages of the IVF process?
1. Follicles are stimulated using gonadotropins (many are stimulated)
2. Mature eggs are removed from the ovaries before the follicle ruptures.
3. Eggs are fertilised with sperm
4. Fertilised embryos are grown in the laboratory in vitro and are subsequently replaced in the uterus.
140
How is a blastocyst formed?
Cleavage of blastomeres in mammals results in some cells enclosed within the inner compartment of the morula.
Fluid begins to accumulate between the blastomeres through Na+/K+ ATPase activity (Na+ and K+ pumped into space, water follows by osmosis - active transport). This is cavitation and results in formation of a blastocoel, and thus a blastocyst.
141
What is zona hatching?
The zona pellucida prevents cell-cell contact of the embryo in the oviduct wall. In the uterus, hatching of the zona occurs just prior to implantation. The blastocyst secretes enzymes which lyses the zona, allowing the embryo to implant.
142
What are some of the major changes in embryo metabolism before implantation?
The zygote is relatively quiescent and possesses a limited capacity to utilise glucose. Instead, it generates energy from low levels of pyruvate oxidation and/or lactate with asparate.
The blastocyst is conversly very metabolically active and has a high capacity to utilise glucose. It generates energy both from aerobic glycolysis and the oxidation of glucose. It uses energy to actively transport organic molecules and ions.
143
How does implantation occur?
The embryo loses the zona and the glycocalyx.
The trophoblast comes into direct contact with the uterine epithelium, causing a decidual reaction in the stroma and vascular changes.
The trophoblast cells start to penetrate the epithelium, decidua, and up to 1/3 of the myometrium. They target maternal blood vessels and degrade them to provide adequate blood supply to the growing foetus and placenta.
144
How does the grey crescent come into being?
In amphibian eggs, the animal cortex is pigmented while the vegetal cortex is not.
Sperm have specific binding sites in the animal pole, and on binding of the sperm, the cortical cytoplasm rotates towards the site of sperm entry, causing the pigment to shift.
145
How does fertilisation activate development?
The centriole from the sperm initiates cytoplasmic reorganisation, and causes microtubules in the vegetal to form a parallel array to guide the cytoplasm.
As the cytoplasm moves, developmental signals are distributed: B-catenin and GSK-3 are distributed throughout the cytoplasm, while a GSK-3 inhibitor which originates in the vegetal cortex moves along microtubules to the grey crescent, where it prevents degradation of B-catenin.
The result is a higher concentration of B-catenin in the dorsal region-cytoplasmic segregation of transcription factors.
146
What is the response to a decrease in blood pressure?
A decrease in blood pressure is detected by baroreceptors in the carotids and aorta which initiate a response to return the mean arterial pressure to normal. The sympathetic nervous system is invoked to increase heart rate and vasoconstriction, as well as venous return. The endocrine system also acts in the form of the RAAS pathway, which causes vasoconstriction, increases water reabsorption and stimulates thirst.
147
What is the response to an increased demand for oxygen?
An increased demand for oxygen is detected by chemoreceptors in the carotids and aorta (O2), and medulla (CO2) which activate the autonomic nervous system to divert blood flow to the muscles. Hormones such as norepinephrine (neuro), endothelin (paracrine) and angiotensin II are released to stimulate vasoconstriction, whereas bradykinin and nitric oxide stimulate vasodilation. The sympathetic nervous system also increases heart and breathing rate.
