Introduction to Human Physiology-Cell PDF

Introduction to Human Physiology Cell Physiology Cell Physiology Introduction Contents Cell structure and composition Function of cellular organelles Structure and function of the cell membrane: Cellular connections & communication...

Introduction to Human Physiology Cell Physiology Cell Physiology Introduction Contents Cell structure and composition Function of cellular organelles Structure and function of the cell membrane: Cellular connections & communication Cellular environment: Body fluids & electrolyte balance Transport across the cell membrane Diffusion Active transport + Bulk transport Physiological adjustment mechanisms of the body Homeostasis + Allostasis + Heterostasis 11/7/2024 2 Cell Physiology Introduction The Cell Cell is the smallest, self-replicating unit of integrated physiological function In a complex, multi-cellular organism, each cell has specialized functions, and no one cell is able to perform all of the tasks required to maintain the organism i.e. the functional integration of the organism is the result of interactions between specialized cells 11/7/2024 3 Cell Physiology Introduction The Cell Component ideas of the cell: 1. Plasma membrane serves as a permeability barrier of the cell and determines what can enter and leave the cell 2. Constituents and state of the ECF and ICF are different 3. All cells have the same DNA, however not all genes are expressed in every cell Thus, cells have many common functions but also many specialized functions 11/7/2024 4 Cell Physiology Introduction The Cell Component ideas of the cell: 4. The organism is composed of cooperating cells, with each cell type contributing its special functions to the integrated performance of the organism 11/7/2024 5 Cell Physiology Introduction The Cell Composition: CHOs → ≈ 3% of the dry mass of a typical cell Lipids → ≈ 40% of the dry mass of a typical cell Proteins → ≈ 50-60% of the dry mass of a typical cell Nucleic acids → DNA + RNA 11/7/2024 6 Cell Physiology Introduction The Cell Functions: Obtaining food and O2 from its surrounding Elimination of waste products Performing various chemical reactions Synthesis of materials for cellular structure, growth and cellular functions Sensitivity and responsiveness to changes in its immediate surrounding 11/7/2024 7 Cell Physiology Introduction The Cell Functions: Reproducing (most cells except nerve and muscle cells) Moving materials in and out of the cell and within the cell in carrying out cellular activities The cell membrane serves as the site of signal transduction → a process by which a cell converts an input signal into a response 11/7/2024 8 Cell Physiology Introduction Cell Organelles Non-membrane limited: Membrane limited organelles: Chromosomes Nucleus Nucleoli Endoplasmic reticulum (ER) Ribosomes Golgi apparatus (GA) Microtubules Lysosomes Microfilaments Mitochondria Centrioles Peroxisomes 11/7/2024 9 Cell Physiology Introduction Cell Organelles 11/7/2024 10 Cell Physiology Introduction Cell Organelles Plasma Membrane 7.5nm thick, Composed of a phospholipids bilayer and protein Selective barrier to movement of ions/molecules into & out of cell Mitochondria Rod-or oval-shaped bodies surrounded by two membranes. Major site of ATP production, oxygen utilization, and CO2 formation. Contains enzymes of Krebs cycle and oxidative phosphorylation 11/7/2024 11 Cell Physiology Introduction Cell Organelles Endoplasmic Reticulum 1 interconnected cell organelle Two opposed membranes separating a space Granular ER Ribosomal particles bound to ER membrane Synthesis of proteins to be secreted from cell Agranular ER No ribosomes Fatty acid and steroid synthesis Calcium storage and release in muscle cells 11/7/2024 12 Cell Physiology Introduction Cell Organelles Golgi apparatus Cup-shaped series of closely opposed membranous sacs and vesicles Concentration and modification of proteins prior to secretion Secretory vesicles Membrane-bound sacs containing concentrated solution of proteins Protein secretion 11/7/2024 13 Cell Physiology Introduction Cell Organelles Lysosomes Density staining oval body surrounded by membrane Contains hydrolytic enzymes Digestive organelle Specialized for breakdown of engulfed bacteria and damaged cell organelles Peroxisomes Play important roles in metabolism, ROS detoxification 11/7/2024 14 Cell Physiology Introduction Cell Organelles Free Ribosomes 20-nm-diameter particles composed of RNA and protein. Not bound to membranes. Site at which amino acids are assembled into proteins. Site at which proteins to be used intracellular are assembled 11/7/2024 15 Cell Physiology Introduction Cell Organelles Bound Ribosomes/filaments Bound to membranes of granular endoplasmic reticulum. 5-15nm diameter protein threads of variable length Site at which proteins to be secreted from cell are assembled. Cell movements. Also used to provide structural support at cell junctions 11/7/2024 16 Cell Physiology Introduction Cell Organelles Microtubules 25nm diameter protein tubules with 15nm diameter hollow core Maintenance of cell shape (cytoskeleton) Associated with movements of cilia, flagella, and mitotic spindle Centrioles Two small cylindrical bodies composed of nine sets of three fused microtubules Formation of spindle apparatus at poles of cell during cell division. Also associated with formation and movement of cilia 11/7/2024 17 Cell Physiology Introduction Cell Organelles Granules Aggregated of crystals of chemical substances Storage of specialized end products of metabolism Glycogen granules are most common Fat droplets Spherical globule of triacylglycerol Storage of fat 11/7/2024 18 Cell Physiology Introduction Cell Organelles Nuclear envelope Surrounds the nucleus Two opposed membranes separating small space Nuclear pores: 50-70 nm diameter Barrier to movement of most molecules. Messenger RNA passes to cytoplasm through pores 11/7/2024 19 Cell Physiology Introduction Cell Organelles Chromatin Coiled threads composed of DNA and protein 46 strands per human cell nucleus DNA stores genetic information. Chromatin condenses into chromosomes during cell division Nucleolus Coiled filamentous structure associated with granules Not surrounded by membrane Site of ribosomal RNA synthesis 11/7/2024 20 Cell Physiology Introduction Cell Membrane Composition: 1. Lipids → Phospholipids + Cholesterol 2. Proteins → Peripheral + Integral 3. CHOs → Polysaccharides 11/7/2024 21 Cell Physiology Introduction 11/7/2024 22 Cell Physiology Introduction 11/7/2024 23 Cell Physiology Introduction 11/7/2024 24 Cell Physiology Introduction Cell Membrane 1. Lipids a. Phospholipids → Amphiphilic/amphipathic Constitute the majority of membrane lipids Have a glycerol backbone (the hydrophilic head) + two fatty acid tails (hydrophobic) Hydrophobic tails face each other and form a bi-layer Lipid-soluble substances (O2, CO, steroid hormones…) can dissolve in the hydrophobic lipid bi-layer and cross cell membranes easily 11/7/2024 25 Cell Physiology Introduction Cell Membrane a. Phospholipids → Amphiphilic/amphipathic Water-soluble substances (Na+, Cl-, glucose, H20…) cannot dissolve in the lipid of the membrane, but may cross through water-filled channels/pores, or may be transported by carriers b. Cholesterol Long rigid hydrophobic chain and a small polar hydroxyl group Maintain the integrity + fluidity of the cell membrane Helps to prevent the membrane from becoming too fluid + too firm 11/7/2024 26 Cell Physiology Introduction Cell Membrane b. Cholesterol Long rigid hydrophobic chain and a small polar hydroxyl group Interacts with the fatty acid tails and functions to immobilise the outer surface of the membrane (reducing fluidity) It functions to separate phospholipid tails and so prevent crystallisation of the membrane It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross It helps secure peripheral proteins by forming high density lipid rafts capable of anchoring the protein 11/7/2024 27 Cell Physiology Introduction Cell Membrane 2. Proteins: a. Peripheral (extrinsic) proteins Hydrophilic and readily dissociated from the membrane Not imbedded and not covalently bound to the cell membrane Loosely attached to the cell membrane by electrostatic interactions: Free, floating on the surface (stud the inside and the outside of the membrane) 11/7/2024 28 Cell Physiology Introduction Cell Membrane a. Peripheral (extrinsic) proteins Account for about 30% of the membrane proteins Function as receptors: Bind specific hormones and proteins on the cell membrane Also function as enzymes 11/7/2024 29 Cell Physiology Introduction Cell Membrane b. Integral (intrinsic) proteins Tightly associated with membrane → anchored to and imbedded in the cell membrane through hydrophobic interactions Partly hydrophilic (polar and protruding to cell surface) and partly hydrophobic (non-polar and embedded in the lipid bilayer) Exist as separate globular units running through the width of the cell membrane Protruding part may often carry CHO chains or lipids attached to their tips 11/7/2024 30 Cell Physiology Introduction Cell Membrane b. Integral (intrinsic) proteins Account for about 70% of the membrane proteins Serve as: Receptors + Ion channels Transport proteins (carriers) Enzymes + GTP-binding proteins (G proteins) Many of them provide structural channels/pores through which water molecules and water-soluble substances, especially ions can diffuse in and out of the cell 11/7/2024 31 Cell Physiology Introduction Cell Membrane Ion channels: Leak channels → continuously open Voltage gated Ligand gated: External ligand → hormones, neurotransmitters… Internal ligand → Ca++, cAMP, G-proteins… Mechanically gated → mechanical force 11/7/2024 32 Cell Physiology Introduction 11/7/2024 33 Cell Physiology Introduction Cell Membrane 3. Carbohydrates Hydrophilic polysaccharides covalently linked to proteins (glycoproteins) or lipids (glycolipids) Function as cell recognition markers and adhesion Cell-cell signaling or Cell-pathogen interactions Structural role as a physical barrier 11/7/2024 34 Cell Physiology Introduction Intercellular Connections a. Tight junctions (zonula occludens) Intercellular adhesion complexes that control paracellular permeability (size and charge-selective) Tight (impermeable) → renal distal tubule Leaky (permeable) → renal proximal tubule and gallbladder Form the border between the apical and basolateral cell surface domains in polarized epithelia → maintenance of cell polarity by restricting intermixing of the two domain components 11/7/2024 35 Cell Physiology Introduction Intercellular Connections b. Gap junctions Clusters of intercellular channels that allow direct diffusion of ions and small molecules between adjacent cells Formed by head-to-head docking of hexameric assemblies (connexons) of tetraspan integral membrane proteins (connexins) Formed by two connecting trans-membrane protein rings (connexins) Permit changes in membrane potential (action potential) to pass from cell to cell 11/7/2024 36 Cell Physiology Introduction Intercellular Connections c. Desmosomes Intercellular junctions that tether intermediate filaments to the plasma membrane Critical for maintaining stable cell–cell adhesion Found in tissue that experience intense mechanical stress, such as cardiac muscle, bladder, gastrointestinal mucosa, and epithelia 11/7/2024 37 Cell Physiology Introduction Intercellular Connections d. Adherence junctions (zonula adherens) Cell-cell adhesion complexes that are continuously assembled and disassembled, allowing cells within a tissue to respond to forces, biochemical signals and structural changes in their microenvironment Provide strong mechanical attachments b/n adjacent cells like cardiac muscle cells 11/7/2024 38 Cell Physiology Introduction Cellular Communication Almost all cells sense their environment primarily by detecting chemical or electrical signals probably by employing surface proteins (receptors) embedded within the plasma membrane Mechanisms of chemical signaling: Autocrine Paracrine Synaptic Endocrine and Neuroendocrine 11/7/2024 39 Cell Physiology Introduction 11/7/2024 40 Body Fluid Composition & Electrolyte Balance Cell Physiology Introduction Body Fluid Composition Body Fluid Compartments The plasma membrane divides the cell into compartments with specific biochemical compositions and functions Each fluid compartment has the optimal biochemical composition to enable a different set of physiological processes to occur Many cellular processes take place in or on the membranes of organelles 11/7/2024 42 Cell Physiology Introduction Body Fluid Composition Body Fluid Compartments Processes tend to alter composition within the compartments For normal survival to continue, alterations beyond the normal range are resisted by homeostasis: i.e., transport processes operate continuously to adjust and maintain constancy of the internal environment Fluid compartments: Intracellular compartment (ICF) Extracellular compartments (ECF) 11/7/2024 43 Cell Physiology Introduction Body Fluid Composition Almost two-thirds of the body (≈ 60%) is composed of water 1. Extra-cellular Fluid (ECF) Constitutes about 20% of body weight (14L) ≈ 1/3 of TBW Fluid in the vascular system ≈ 25% of ECF Fluid in the interstitium ≈ 75% of ECF Fluid in the transcellular space ≈ 0.5 litre 2. Intra-cellular Fluid (ICF) ≈ 40% of body weight (28L) ≈ 2/3 of TBW 11/7/2024 44 Cell Physiology Introduction 11/7/2024 45 Cell Physiology Introduction Body Fluid Compartments IC fluid EC fluid Exchange much more selective Interstitial fluid plasma Relatively free exchange Cell Physiology Introduction Body Fluid Compartments 11/7/2024 47 Cell Physiology Introduction Body Fluid Composition Ion distribution Cations: Major ion in ECF = Na+ Major ion in ICF = K+ Na+-K+ pump helps to: Push out Na+ that leaks into cells Push in K+ that leaks out of cells 11/7/2024 48 Cell Physiology Introduction Body Fluid Composition Ion distribution Anions: Main ICF anions → large organic molecules (Proteins, Phosphates) (remain inside the cell , they are too large to diffuse out) Main ECF anions → Cl-, HCO3- Since many cellular anions cannot diffuse out, Cl- tends to stay mainly outside the cells The Donnan effect 11/7/2024 49 Cell Physiology Introduction 11/7/2024 50 Cell Physiology Introduction 11/7/2024 51 Cell Physiology Introduction Distribution of Solutes is based on: Electrochemical activity Osmotic activity Distribution of ions leads to the development of: Electrical activity on the cell surface Osmotic pressure in cell compartments 11/7/2024 52 Transport across the Cell Membrane Cell Physiology Introduction Transport Mechanisms Types of transport mechanisms: 1. Passive transport 2. Active transport 3. Bulk transport 11/7/2024 54 Cell Physiology Introduction Transport Mechanisms 1. Passive transport Involves physiochemical forces that do not require metabolic energy Simple and facilitated diffusion a. Simple Diffusion Free movement of a substance from one part of a solution to another occurring in both directions Net movement occurs from an area of high concentration to another area of low concentration 11/7/2024 55 Cell Physiology Introduction Transport Mechanisms Factors affecting rate of diffusion Viscosity of solution Mol. wt → light molecules diffuse faster Lipid solubility → lipid soluble molecules can easily cross the cell membranes Electrical charge and electrical gradient Charged molecules move faster in the direction of the opposite charge and slower or not at all in the direction of the same charge Unionized molecules with low concentration on opposite side of the membrane diffuse rapidly in that direction 11/7/2024 56 Cell Physiology Introduction Transport Mechanisms b. Facilitated diffusion Occurs down an electrochemical gradient ("downhill"), similar to simple diffusion Does not require metabolic energy (passive) More rapid than simple diffusion (carrier-mediated) Exhibits – stereo-specificity, saturation and competition 11/7/2024 57 Cell Physiology Introduction Transport Mechanisms Osmosis: Passive fluxes of water across a membrane High conc. of solute on one side Lower diffusional permeability of solute across the membrane Filtration → fluid is forced through a membrane because of pressure difference on the two sides 11/7/2024 58 Cell Physiology Introduction Transport Mechanisms 2. Active transport Utilizes metabolic energy Primary active transport a. Na+-K+ ATPase (Na+-K+ pump) b. Ca2+ ATPase (Ca2+ pump) c. H+- K+ ATPase (proton pump)… Secondary active transport Na+-glucose co-transport Na+-H+ counter-transport Na+-Ca2+ exchanger H+-Oligopeptide transport Na+-K+-2Cl- co-transport H+-NT exchanger 11/7/2024 59 Cell Physiology Introduction Transport Mechanisms a. Na+-K+ ATPase (Na+-K+ pump) Transports 3Na+ from ICF to ECF and 2K+ from ECF to ICF Maintains low intracellular [Na+] and high intracellular [K+] Transported against their concentration gradients. NB Cardiac glycoside drugs (ouabain + digitalis) specifically inhibit Na+-K+ ATPase 11/7/2024 60 Cell Physiology Introduction Transport Mechanisms b. Ca2+ ATPase (Ca2+ pump) Located in the sarcoplasmic reticulum (SR) + the cell membrane Transports Ca2+ from the ICF to the SR + ECF (against electrochemical gradient) c. H+- K+ ATPase (proton pump) In gastric parietal cells transports H+ into the lumen of the stomach against its electrochemical gradient Proton pump inhibitors (Omeprazole, Pantoprazole…) 11/7/2024 61 Cell Physiology Introduction Transport Mechanisms Secondary active transport Does not directly require energy (ATP) Uses an electrochemical gradient (generated by active transport) as an energy source to move molecules against their gradient. A transporter protein couples the movement of an ion (typically Na+/H+) down its electrochemical gradient to the uphill movement of another molecule/ion 11/7/2024 62 Cell Physiology Introduction Transport Mechanisms Secondary active transport: types Cotransport/Symport Na+/glucose cotransport Na+ -K+ -2Cl- cotransport Exchange/antiport Na+/Ca2+ exchanger Na+/H+ counter-transport H+/oligopeptide transporter H+/NT exchanger 11/7/2024 63 Cell Physiology Introduction 11/7/2024 64 Cell Physiology Introduction 11/7/2024 65 Cell Physiology Introduction 11/7/2024 66 Cell Physiology Introduction Transport Mechanisms Secondary active transport NB The energy for 2° active transport is derived from the "downhill" movement of the drive ion (Na+/H+) The electrochemical gradient of the drive ions is maintained by 1° active transport Dysfunction of the 1° active transporter secondarily affects the 2° active transport 11/7/2024 67 Cell Physiology Introduction Transport Mechanisms 3. Bulk transport Transport of larger molecules Uses metabolic energy Endocytosis + Exocytosis 11/7/2024 68 Cell Physiology Introduction Transport Mechanisms a. Endocytosis Engulfing of materials by invaginating the outer part of a cell membrane until it buds off within the cytoplasm It can be: Phagocytosis → “cell eating ” Large molecules such as bacteria, dead RBC… surrounded by cell membrane and taken up Pinocytosis 11/7/2024 69 Cell Physiology Introduction 11/7/2024 70 Cell Physiology Introduction Transport Mechanisms a. Endocytosis Pinocytosis → invagination occurs into cell and pinches off to form boundary of an intracellular vesicle, vacuole or tubule (absorption of undigested protein in the gut of newborns…) Pinocytosis may be: Fluid endocytosis → enclosing a small volume of ECF or Adsorptive endocytosis → specific molecules bound to cell membranes and carried into cell 11/7/2024 71 Cell Physiology Introduction Transport Mechanisms b. Exocytosis Emeiocytosis → “Cell vomiting” Release of neurotransmitters, digestive enzymes and some hormones… 11/7/2024 72 Cell Physiology Introduction 11/7/2024 73 Introduction to Human Physiology Physiological Adjustment Physiological Adjustment Introduction Introduction Individual functions of all the body’s different cells + tissues + organs are integrated into a functional whole → the human body These separate organs and systems are coordinated to maintain proper function of the entire body A vast network of feedback controls are involved to achieve the necessary balances Physiological Adjustment mechanisms: Homeostasis → Maintaining constancy Allostasis + Heterostasis → changing to cope up with prevailing conditions 11/7/2024 75 Physiological Adjustment Homeostasis Homeostasis The tendency of biological systems to maintain a state of equilibrium A process that maintains the internal environment of living systems in a more or less constant state May be occasionally interrupted when a stressor is perceived and a fight- flight response is in effect Measured values are compared with a pre-determined "set point“ Error signal → the difference between measured values and pre- determined set point The error signal is used to generate signals that help return the regulated variable toward its pre determined value 11/7/2024 76 Physiological Adjustment Homeostasis Homeostasis Component ideas of Homeostasis The organism normally maintains a more or less constant internal environment that is different from the external environment Stability of the internal environment occurs via information flow in the form of negative feedback Assaults on life derive not only from the external environment but also from the internal environment of the body In effect, living organisms continue to survive by adjusting to environmental changes by regulation and adaptation 11/7/2024 77 Physiological Adjustment Homeostasis Homeostasis Regulation Both intrinsic and extrinsic Intrinsic regulation: Occurs in cell/tissue/organ These body components adjust themselves intrinsically to environmental changes They are also adjusted by extrinsic regulation Extrinsic regulation Involves nervous + endocrine systems that constitute long distance communication systems 11/7/2024 78 Physiological Adjustment Homeostasis Homeostasis Extrinsic regulation Nervous system → Rapid adjustment to changes Endocrine system → slower but long lasting metabolic adjustment Neuro-endocrine → integrated in many instances to provide optimal environment for the cell: Neurohypophyseal system → hypothalamus – pituitary gland Autonomic – endocrine system → SNS – Adrenal gland 11/7/2024 79 Physiological Adjustment Homeostasis Homeostasis Components of Homeostasis Set point → predetermined reference value Receptor → detects changes Afferent path → transmits signal from the receptor to an integrating center through afferent nerves or hormones Integrating center → assess and discriminate the transmitted signal using a reference or set value Efferent path → transmit the discrepancy (error signal) that occurs to effector organs through efferent nerves Effector organ → respond in accordance with the need for adjustment 11/7/2024 80 Physiological Adjustment Homeostasis Feedback mechanism Negative feedback Positive feedback Feed forward mechanism 11/7/2024 81 Physiological Adjustment Homeostasis Negative Feedback Output returns to the normal input → response is in the opposite direction as the stimulus The system is restored back to its original state by resisting or opposing any attempts to change the system → “The law of sheer cussedness” favoring stability 11/7/2024 82 Physiological Adjustment Homeostasis Negative Feedback Regulation of Temperature Regulation of PaCO2 Regulation of Blood pressure Regulation of hormonal secretion Regulation of blood glucose Regulation of effective circulating volume 11/7/2024 83 Physiological Adjustment Homeostasis Positive Feedback Output is not returned to the normal input: i.e. response is in the same direction as the stimulus May be part of a negative feedback mechanism Rare in biology because in many cases, it causes instability leading to death, i.e. it favors instability 11/7/2024 84 Physiological Adjustment Homeostasis Positive Feedback Includes: Nerve impulse LH secretory surge Uterine contraction during labor Severe shock Viral infection: virus invades cell replicates in cell many viruses invasion of other cells further replication 11/7/2024 85 Physiological Adjustment Homeostasis Feed forward mechanism Disturbance is sensed and corrective measure is taken in anticipation of a change Feed forward mechanism anticipates changes For example, heart rate and breathing increase before a person begins to exercise Feed forward may be positive or negative but usually operates in combination with negative feedback mechanisms, e.g. in doing an exercise 11/7/2024 86 Physiological Adjustment Allostasis Allostasis Maintenance of stability and viability through change in the face of stress challenge to represent acute stress response Highlights our ability to anticipate, adapt to, or cope with impending future events Allostasis literally means maintaining stability (or homeostasis) through acute change, i.e. attaining viability through change It addresses basic regulatory systems and examines the behavior of bodily regulation under duress 11/7/2024 87 Physiological Adjustment Allostasis Allostasis With allostatic regulation by cephalic involvement, the body adapts to potentially diverse and dangerous situations through the activation of neural, hormonal, or immunological mechanisms Various types of stress mediators such as catecholamines and cortisol are used in the process of Allostasis 11/7/2024 88 Physiological Adjustment Allostasis Allostasis Load Allostatic load refers to the cost of adaptation to a stressful environment eliciting repeated and sometimes prolonged adaptive responses Repeated cycles of allostasis and inefficient turning- on or shutting off of responses lead to wear and tear (allostatic load) of the body Manifestations of allostatic load include: Decreased cognitive function during aging, Abdominal obesity, an increased risk for hypertension and cardiovascular disease, Insulin-dependent diabetes, and Decreased immune responses, etc. 11/7/2024 89 Physiological Adjustment Allostasis Allostasis Load The concept of allostasis and allostatic load envisions a cascade of cause and effect that begins with primary stress mediators such as catecholamines i. Overstimulation by frequent stress, resulting in excessive stress hormone exposure ii. Failure to inhibit allostatic responses when they are not needed or an inability to habituate to the same stressor, both of which result in overexposure to stress hormones; and 11/7/2024 90 Physiological Adjustment Allostasis Allostasis Load iii. Inability to stimulate allostatic responses when needed, in which case other systems (e.g., inflammatory cytokines) become hyperactive and produce other types of wear and tear Allostasis and Happiness There is also a strong connection between allostasis and happiness with happiness there are alterations in various physiological parameters like heart rate, blood pressure, etc. 11/7/2024 91 Physiological Adjustment Heterostasis Adaptation (Heterostasis) Adjusting by changing chemically and structurally on a long-term basis External world problems to be solved structural evolutionary changes to solve problems of existence adaptation 1. Long-term adaptation to cold 25-50% loss in BMR cooling of peripheral and deep lying tissues average skin temp. up to 15-12o C→ gradient of heat flow reduced Thermal conductivity drops from 8 kcal/m2/hr/oc to 5 kcal temp. gradient reduced heat loss 11/7/2024 92 Physiological Adjustment Heterostasis Heterostasis 2. Long term Adaptation to heat Activity of sweat glands: Temperate climate some sweat glands are inactive reduced ability of sweating Hot climate all sweat glands become active increased ability of sweating Genetic adaptation Body shape Long limbs 11/7/2024 93 Physiological Adjustment Heterostasis Heterostasis 3. Adaptation to high altitude Hyperhaemoglobinaemia Hypervascularization Hyperactivity of cell enzymes → ↑O2 utilization 11/7/2024 94 Physiological Adjustment Heterostasis Heterostasis 3. Adaptation to high altitude Birds are more adaptable to high altitudes because of high cardiac output and more efficient respiratory system Mammals are rarely found at about 6000 metres above sea level but some birds nest at 6500m and others migrate above 9000m The physiological adjustment is in P50 and not in Hct There are homeostatic and adaptive changes in organ systems including respiratory, cardiovascular/blood, endocrine and neural changes 11/7/2024 95