Mammalian Biology Study notes PDF

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Mammalian Biology Objectives Lecture 2 Teleology: theory that all natural things are designed to fulfil a particular purpose Shapes of animals are determined by a combination of selection forces imposed by the environment and physical laws Marine mammals  Streamline  Relatively straight spine beca...

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Mammalian Biology Objectives Lecture 2 Teleology: theory that all natural things are designed to fulfil a particular purpose Shapes of animals are determined by a combination of selection forces imposed by the environment and physical laws Marine mammals  Streamline  Relatively straight spine because water supports weight  Same muscle for breathing and locomotion Quadrupeds  Spine C-shaped, transfers weight to legs  Weight on shoulders, not thorax Carnivores  Spine curves upwards as they bring their feet together underneath them  Eyes facing forward Herbivore  Heavier skeleton required to support weight of herbage in digestive tract Bipeds  Upright posture, bipedal motion  S-shaped spine  Coastal muscles only for breathing  Other mechanical factors that aid in bipedal motion, include a locking knee joint, broad pelvis etc.  Eyes in front  Co-ordinate breathing independently An animals size and shape have a direct effect on how the animal exchanges energy and materials with its surroundings Exchange with the environment occurs as substances dissolved in the aqueous medium diffuse or are transported across the cells plasma membrane Cells need a closely regulated environment for optimum activity of biochemical reactions and cell structural integrity Cells must be able to  Obtain fresh supplies of substrates  Store or export products  Eliminate wastes Advantages of single cell  If constant external environment single-celled organisms may use simple diffusion because of high ratio of surface area to volume  Do not require complex support or strengthening structures  Cell membrane  Osmotic pressure  Reproduce by mitosis

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 Don’t need independent movement Problems of large cell size An individual mass of protoplasm is physiologically and structurally ineffective if too large  Lack of mechanical strength  Insufficient surface area  Internal transport is too slow  Reproduction is more difficult  Internal communication is less effective  Coordination between the parts is poor As a result, large animals are necessarily multicellular To overcome these problems, the multicellular animal has evolved groups of specialised cells called tissues and organs to carry out the specific functions required to maintain a stable internal environment Connective, muscle, epithelia, nervous

Organ Heart Lungs Liver Kidney Stomach Intestines Pancreas Spleen Reproductive organs Brain Skin

Organ system Circulatory Respiratory Endocrine Skeletal Urinary Digestive Nervous Musculature Immune Mammary Skin

Internal exchange surfaces  Respiratory system  Digestive system  Excretory system Mammals may be considered to be a tube within a tube. The lumen of the digestive tract is actually outside of the animals. Similarly, the inner surfaces of the lugs, kidney and uterus are outside. Organs hang within body (coelomic) cavities that permit expansion and movement of the organs The cavities containing the organs are Dorsal cavity  Cranial cavity-brain  Spinal cavity-spinal cord Ventral cavity  Thoracic cavity-heart and lungs 2

Abdomino-pelvic cavity-contains the liver, kidneys, reproductive and urinary tracts. Each cavity and its organs have their own named serosa:  Pleura-serosa lining cavity around the lungs  Pericardium-serosa lining cavity around the heart  Peritoneum-serosa lining abdominal and pelvic cavities

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Due to the cell fate, which is progressively more influenced by signals from surrounding cells. This process termed induction also causes changes in gene expression so that cells of the embryo become progressively more different Stem cells important as continuously dividing to replace the cells that die and are continuously lost Holistic approach: the interaction of these systems can only be evaluated by looking at the whole animal Reductive approach: can study physiological function of organs to single cells. Progressively more simple systems (can control conditions)

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Organs are a collection of one or more types of tissue. An organ system is a group of organs that work together in performing a body function Connective, muscle, nervous, epithelial. Classified by similar appearance and common function Connective: Consist of sheets of tightly packed cells. Tight junctions between cells forming a barrier to solutes

The shape of epithelial cells can be:  Cuboidal  Columnar  Squamous Arrangement of epithelial cells can be:  Simple (one cell thick)  Stratified (multiple layers of cells)  Pseudostratified (single layer of cells of different heights) Some types of epithelial cells:  Pseudostratified ciliated columnar-respiratory tract  Simple cuboidal-kidney tubules (Absorption)  Stratified columnar-uterus  Stratified squamous-skin, mouth (protection)  Simple squamous-lung alveoli, blood vessels (exchange of gases and ions)  Simple columnar-intestines (excretion) Connective  Holds parts of the body together

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Distributed throughout the body Contain cells called fibroblasts which secrete fibrous proteins, fibres (collagenous, elastic and reticular) and ECM (the jellylike or more solid substances in which cells and fibres are embedded) Connective tissue proper consists of a structureless mass called the ground substances in which cells and ECM fibres are embedded

Muscle (3 types)  Skeletal: under voluntary control by NS  Smooth: Involuntary e.g. food through gut  Cardiac: Involuntary, contraction of heart  All consist of long cells called muscle fibres which contract in response to nerve signals tightly specialised, excitable tissue 

Nervous: Senses stimuli and transmits signals throughout the animal

Lecture 5 

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Microtubules-hollow tubes comprised of dimers of the protein tubulin. Involved in maintenance of the cell shape, motility of cilia and flagella and movement of intracellular components such as organelles and chromosomes (during cell division) Microfilaments-comprised of filaments of the protein actin and are also involved in maintenance and change of cell shape, cell motility and the separation of daughter cells to complete cell division Intermediate filaments-thick cables of tough protein keratin which are involved in the anchorage of intracellular organelles and the linking of cell junctions which anchor epithelial cells to their neighbouring cells Motor proteins-move along the tracks provided by microtubules and microfilaments so that intracellular components can be moved to target sites within cells Tight junctions-seal cells together in an epithelial sheet, May allow water and electrolytes to pass through Anchoring junctions-connect the cytoskeleton of a cell to extracellular contacts e.g. desmosomes Communicating junctions-allows small molecules to pass directly from cell to cell e.g. gap junctions

Some functions of epithelia:  Form glands-single cells or groups of cells specialised for secretion either directly into the bloodstream (endocrine) or via ducts into a cavity (exocrine)  Protection-tight junctions of epithelium control and mostly prevent access of substances into body fluids. Also, some epithelia secrete mucus  Vectorial transport of solutes in one direction

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Secretion of fluid containing digestive enzymes and protective substances Absorption of water and nutrients Movement of lumen contents by cilia, for example in the respiratory tract.

Lecture 6 Water occupies two main fluid compartments.  Intracellular fluid (ICF)-about two thirds by volume, contained in cells  Extracellular fluid (ECF)-comprises the other one third. Made up of  Plasma: the fluid portion of the blood  Interstitial fluid (IF): fluid in spaces between cells  Other ECF: Lymph, cerebrospinal fluid (CSF), eye humours, synovial fluid, serous fluid and gastrointestinal fluid. Diffusion is the tendency for molecules of any substance to spread out evenly into the available space as a result of thermal motion Osmosis is the movement of water across a semi-permeable membrane. Osmoregulation depends on the controlled movement of solutes so that water follows by osmosis. Solutes in solution attract water molecules, which form a hydration shell. All mammalian cells have an electrical potential difference across plasma membrane. The cytoplasmic side is negatively charged relative to the extracellular side. The resting membrane potential results from the Na+ and K+ concentration gradients across the membrane and the greater permeability of the plasma membrane to K+ than to Na +. Since K+ concentration inside the cell is much higher than outside, its higher permeability than that of Na+ means that there is a net flux of positive charges out of the cell and therefore the intracellular fluid close to the plasma membrane from where the K+ movement occurs has a net negative charge relative to the region close to the membrane on the extracellular side. This is the source of the resting membrane potential Facilitated diffusion Many hydrophobic substances diffuse through membranes with the assistance of transport proteins, either channel or carrier proteins  A channel protein has a specific channel through which water molecules or a specific solute can pass  A carrier protein alternates between two conformations, moving a specific solute across the membrane as the shape of the protein changes Active transport All mammalian cells maintain a low intracellular concentration of sodium relative to the extracellular fluid and high intracellular potassium by pumping these ions against their large concentration gradients. Active transport requires energy either by ATP or by using the existence of another concentration gradient The sodium-potassium pump: a specific case of active transport 1. Cytoplasmic Na+ binds to the sodium-potassium pump 2. Na+ binding stimulates phosphorylation by ATP

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3. Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside 4. Extracellular K+ binds to the protein, triggering release of the phosphate group 5. Loss of the phosphate restores the proteins original conformation 6. K+ is released and Na+ sites are receptive again, the cycle repeats

Ion Channels Two forces affect the movement of charged particles (ions) across the cell membrane, their charge (electrical) and their relative concentration on either side (chemical gradient) A number of different ion channels are present in the membrane of cells. Ion channels can be either open or closed so that a particular ion either passes through the channel or does not. Ion movement depends upon the combined electrochemical gradient Ion channels can be either always open, in which case they are referred to as leakage channels or they can be gated. Example-nerve cells have more K+ than Na+ leakage channels so that resting membrane potential is -70mV Gated channels can be opened or closed b a change in the conformation of the protein that forms the channel. This change in conformation can be triggered by one of several events 1. Electrical potential-membrane potential affects the activity of excitable cells and the transmembrane movement of ions 2. Chemical agonists and antagonists 3. Mechanical stimuli, light and changes in cell volume Lecture 7 Blood is comprised of a number of different cell types suspended in plasma Functions of blood:  Respiratory gas exchange  Regulatory activity-metabolic regulation (hormone transport), maintenance of pH in tissues, regulation of body temperature  Distribution of nutrients  Excretion of metabolic end products  Carrier for immunological protective agents Blood plasma is about 90% water Contains many important solutes  Electrolytes-inorganic salts in the form of dissolved ions  Plasma protein-influence blood pH, osmotic pressure and viscosity. Function in lipid transport, immunity and blood clotting Suspended in blood plasma are two classes of cells  Red blood cells, which transport oxygen  White blood cells, which function in defence  A third cellular element, platelets are fragments of cells and are involved in clotting

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Red blood cells (erythrocytes)  Transport oxygen throughout the body  Help transport CO2 White blood cells  Neutrophils-phagocytose and destroy bacteria  Eosinophils-destroy larger parasites and modulate allergic inflammatory responses  Basophils-release histamine in certain immune response  Monocytes-Become tissue macrophages, which phagocytose and digest invading microorganisms and foreign bodies as well as damaged senescent (cannot divide) cells.  Lymphocytes  B lymphocytes-make antibodies  T lymphocytes-Cytotoxic T-cells: Kill infected and tumour cells. T-helper cells: Regulate immune response  Natural killer cells-Kill virus-infected cells and some tumour cells  Initiate blood clotting

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Neutrophils and macrophages  Can be found migrating through the body  Can be found in various organs of the lymphatic system  Are phagocytic white blood cells that can engulf and digest foreign cells and unwanted matter 2 types of lymphocytes B lymphocytes (mature in the bone marrow)-humoral response  Recognise and bind to an antigen, undergo clonal expansion, produce two types of daughter cells, memory cells and plasma cells  Plasma cells synthesis and secrete large amounts of antibody which attack pathogens displaying exactly the same antigen T lymphocytes (mature in the thymus)-cell-mediated response 3 subsets-Cytotoxic T cells, helper T cells and regulatory T cells Cytotoxic T cells produce toxic substances that kill our body’s own cells, when these have become infected or mutated

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Lecture 8 The cardiac cycle is one cycle of contraction or systole (pumping) and relaxation or diastole (filling). The volume of blood pumped out from the left ventricle in one minute is cardiac output (CO). Cardiac output depends on the heart rate (beats per minute) and the amount of blood pumped by the left ventricle in each contraction i.e. stroke volume (SV). CO=HRxSV Blood pressure is the hydrostatic pressure that blood exerts against the wall of a vessel Systolic pressure is the pressure in the arteries during ventricular systole and is the highest pressure in the arteries Diastolic pressure is the pressure in the arteries during diastole and is lower than systolic pressure Blood pressure is determined by cardiac output and peripheral resistance (flow through arterioles is impeded by the narrowness of the arterioles). For instance, during exercise, the arterioles in working muscle dilate which reduces their peripheral resistance so blood flow increases. Blood pressure in veins is low, blood flow returning to the heart is aided by rhythmic contraction of smooth muscle in the vessel walls and the activity of skeletal muscles which squeezes blood through the veins

Blood vessels Arteries and veins:  Outside: connective tissue with elastic fibres, allows vessel to stretch and recoil  Middle layer: smooth muscle and elastic fibres  Inside: lining lumen is endotheliumsingle layer of smooth, flattened cells Capillaries just have endothelium (+ basement membrane)

Systolic pressure

Venae cavae

Veins

Venules

Capillaries

Diastolic pressure

Arterioles

120 100 80 60 40 20 0

Arteries

Velocity (cm/sec)

50 40 30 20 10 0

Aorta

Area (cm2 )

5,000 4,000 3,000 2,000 1,000 0

Pressure (mm Hg)

Some cardiac muscle cells are self-excitory (depolarise spontaneously) and have their own intrinsic contraction rhythm. The sinoartrial node (SAN) or pacemaker region of the heart sets the rate at which all cardiac muscle cells contract. Impulses from the SA pass the atrioventricular node (AVN) in the wall between the right atrium and right ventricle. The impulses are momentarily delayed and then spread through the walls of the ventricles; this means the atria contract fully before the ventricles contract. The spread of the impulses across the ventricles is via specialised muscle fibres (Purkinje fibres) 1. Pacemaker generates wave of signals to contract 2. Signals are delayed at AV node 3. Signals pass to heart apex 4. Signals spread throughout ventricles

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Arteries have thicker walls than veins (accommodate high pressure) Substances exchange between the blood and the interstitial fluid that bathes the cells. Oxygen and carbon dioxide are small molecules and diffuse down their concentration gradients. Blood pressure within the arterial end of the capillary pushes fluid (water and solutes) through the capillary wall. Blood cells and plasma proteins are too large to leave the capillary. The blood proteins within the capillaries create an osmotic pressure difference at the venous end of the capillary, which draws back about 85% of the fluid. The remaining 15% enters the lymphatic system. The lost fluid (15%) enters the tiny lymph capillaries. Overlapping cells, which do not permit fluid to leave. The fluid is propelled by rhythmic contractions by skeletal muscle movement. Lymph nodes within the lymphatic vessels filter the lymph and play an important role in defending against infection. The lymphatic system drains into the circulatory system near the junction of the vena cava with the right atrium. Lecture 9 The nasal cavity leads to the pharynx. On swallowing, the larynx moves upwards so the epiglottis covers the glottis preventing food from entering the airways. Usually the glottis is open so breathing can occur The larynx has cartilage bands and also functions as the voice box. From the larynx, air passes into the trachea, which is held open by C-shaped rings of cartilage. The trachea divides into 2 bronchi leading to each lung. Each bronchus further divides into smaller and smaller bronchioles, which eventually end in air sacs or alveoli. The upper branches of the respiratory tree are protected by cilia and mucus. Defence mechanisms  Vasculature-warmed and moistens air  Mucus blanket and cilia (upper airway)  Branching of bronchial tree (higher chance of coming into contact with mucus)  Phagocytes: macrophages and neutrophils  Secretions-such as immunoglobulins and complement  Irritation response-cough, sneeze etc. The volume of a breath at rest is the tidal volume. The maximum tidal volume is vital capacity. Total lung capacity is greater than vital capacity as it is not possible to empty the lungs completely, the residual volume remains in the lungs. Dead space is the portion of each tidal volume that does not take part in gas exchange. Control of breathing The centres in the medulla and pons  Regulate the rate and depth of breathing in response to pH changes in the cerebrospinal fluid  The medulla adjusts breathing rate and depth to match metabolic demands Sensors in the aorta and carotid arteries

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 Monitor O2 and CO2 concentrations in the blood  Exert secondary control over breathing Stretch receptors in lung tissue prevent lungs from over-expanding 1. Carbon dioxide produced by body tissues diffuses into the interstitial fluid and the plasma 2. Over 90% of the CO2 diffuses into red blood cells, leaving only 7% in the plasma as dissolved CO2 3. Some CO2 is picked up and transported by haemoglobin 4. However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalysed by carbonic anhydrase contained within red blood cells 5. Carbonic acid dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+) 6. Haemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thus preventing the Bohr shift 7. Most of the HCO3- diffuse into the plasma where it is carried into the bloodstream to the lungs 8. HCO3- diffuses into the red blood cells from the plasma, combining with H+ released from haemoglobin and forming H2CO3 9. Carbonic acid is converted ba...