Human Biology BIOL1008 Lecture Notes PDF

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Topic 1, 2 & 3: Cell Diversity, Cell Structure & Cell MovementTopic 1: Introduction The world of cells  Human body consists of around 35 trillion cells  Cells in the human body have a short lifetime – billions are made and die every day  There are over 200 different types of cells in the ...

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Topic 1, 2 & 3: Cell Diversity, Cell Structure & Cell Movement Topic 1: Introduction

The world of cells  Human body consists of around 35 trillion cells  Cells in the human body have a short lifetime – billions are made and die every day  There are over 200 different types of cells in the body – each performing different functions  Different types of cells work together to form tissues and organs Types of cells  Nerve cells – connect central nervous system to the rest of the body  Sex cells – sperm and egg are respectively some of the smallest and largest cells in the body  Red blood cells – neat disc shapes, empty of cell contents to carry maximum amount of oxygen to body  Monocytes – hunt down foreign invading cells

Topic 1: Learning Objectives

Learning Objectives  Describe the main compartments of the body, inside-vs-outside, dorsal versus ventral, major body fluid, layers of organisational scale, dimensionality, complexity, dynamic nature of systems, and systems operating together  Explain the major themes organising the human body including scale, concept of surface area to volume ratio and examples of it in operation in the human body including the lungs, digestive tract

Topic 1: Cell Diversity

Organisation and complexity – Key concepts  Theory of evolution by natural selection o Proposed by Charles Darwin & Alfred Wallace o Organisms produce more offspring than are able to survive in their natural environment o Better physically adapted and equipped to survive, grow to maturity and reproduce o Survival of the fittest – those most suited to their environment are most likely to pass on their traits to the next generation  Cell theory o Proposed by Theodor Schwann o All organisms are made up of cells o Cells are the basic units of life o All cells come from pre-existing cells Classes of cells

Prokaryote

Eukaryote

No nucleus

Nucleus

No cytoskeleton

Cytoskeleton

No cytoplasmic organelles

Cytoplasmic organelles

Single circular DNA molecule

Multiple linear DNA molecules

Topic 1: Cell Diversity Cells  Tissues  Organs  Systems  Tissues = complex organisational arrangements of cells to fulfill specific functions  Major groups of tissues: epithelial tissues, connective tissues, muscle tissues, nervous tissues, adipose tissues Explaining the human body 1. Scale (meso, micro, macro) 2. Dimension 3. Complexity (all systems interconnected) 4. Dynamic (multiple processes occurring simultaneously) Processes and regulation of the human body  Acid and base regulation  Surface area to volume ratio  Rapidly absorb and exchange nutrients and waste products with high efficiency  Example: packing of large intestine, structure of small intestine (villi and microvilli) Century of biology  CRISPR used to remove genes  Exoskeletons with motors at hip and knee joints enable people in wheelchairs to walk  Cochlear implants  Bionic eye – retinal implants  Artificial hearts  3D printing of kidney organoids

Topic 2: Learning Objectives

Learning Objectives  Explain how a single cell can survive and function in isolation  Distinguish the main structures and functions of a cell and its main organelles

Topic 2: Cell Structure

Components of a cell  Nucleus: controls activity in the cell  Nucleolus: site of RNA transcription and ribosome biogenesis  Rough endoplasmic reticulum: ribosomes and protein synthesis  Smooth endoplasmic reticulum: lipid and steroid hormone production  Golgi complex: processes and sorts proteins from ER to be moved around cell  Mitochondria: makes ATP, replicates by fission and contains own DNA  Lysosomes: acidic organelles for waste breakdown and disposal  Cytoskeleton: consists of filaments and tubules which provide structure, support and transport

Topic 3: Learning objectives

Learning 

the flow of substances



membranes and the role



emical gradient that

Topic 3: Cell Function

Movement in a cell  Plasma membrane is a phospholipid bilayer  Lipid bilayers are permeable to: o Water molecules o Small uncharged molecules such as oxygen and carbon dioxide  However, lipid bilayers are not permeable to: o Ions such as K+, Na+, Ca2+, Clo Small hydrophilic molecules, such as glucose o Macromolecules such as proteins and RNA Diffusion and osmosis  Diffusion: Particles spread from a highly concentrated area to be equally distributed and eliminate concentration gradients, due to the random motion of particles  Osmosis: Diffusion of water through semi-permeable membrane into another aqueous compartment containing solute at a higher concentration o Water wants to be at equilibrium, where there is the same number of water molecules in each compartment of the cell Tonicity    

Tonicity = osmotic pressure Isotonic = solution with equal osmotic pressure Hypotonic = solution that has higher concentration of water/solvent to solute Hypertonic = solution that has higher concentration of solutes to water

Ion transport  Cell membrane contains transmembrane proteins or integral membrane proteins to transport ions in and out of the cell  These may be either: o Channels (facilitated diffusion) o Transporters (facilitated diffusion or active transport)  Passive = movement down a concentration gradient  Active = movement against a concentration gradient

Topic 3: Cell Function Channels  Pores and channels can become saturated so the rate of movement of ions slows down as concentration of the ion increases  Ion channels also conduct charge, leading to an electrochemical potential difference  We can determine ion concentrations outside the cell through blood tests i.e. level of sodium, potassium and chloride Transporters (facilitated diffusion)  Facilitated diffusion regulates movement of nutrients, such as glucose and amino acids, across the membrane o Uses Na+ as driving force  E.g. GluT transporter to bring glucose into a cell Transporters (active transport)  Sodium potassium pump requires ATP as movement is against concentration gradient  Potassium ions are transported in the cell and sodium ions are transported out of the cell  Uneven movement of charge: 3+ in and only 2+ out  All cells have a negative membrane potential o This is the electrochemical driving force

Endocytosis and exocytosis  Endocytosis = movement of a substance into cell o Material is internalised by cell membrane which buds off inside cell to form a vesicle containing the ingested material  Exocytosis = movement of a substance out of a cell o Vesicle containing material to be egested fuses with the cell membrane and releases material out of cell  Phagocytosis = process where phagocytes engulf or ingest particles

Topic 4 & 5: Cell to Cell & Cell Control

Topic 4: Learning objectives

Learning objectives  Describe the endocrine system and hormones  Explain how hormones allow even distant cells to communicate  Explain the roles of messengers and receptors in cell communication  Describe the difference between lipid soluble and water soluble hormones  Explain the basic mechanism of steroid hormone responses  Explain the difference between first messengers and second messengers, with cAMP as an example

Topic 4: Cell to Cell

Systems to maintain homeostasis  In order to maintain homeostasis, we need systems that control our entire body  The nervous system sends fast electrical messages to cells in the body  The endocrine system sends slower-acting chemical based messages around the body Endocrine system  Endocrine = internal secretion that pertains to a gland that secretes directly into the bloodstream  Endocrine gland = a ductless gland that produces an internal secretion discharged into the blood or lymph and circulated to all parts of the body  Exocrine = external secretion via ducts to epithelial surface  Hormone = chemical/organic molecule messenger made by gland cells that regulates cell activity Functions of hormones 1. Reproduction, growth and development e.g. sex steroids, thyroid hormones, prolactin, growth hormone 2. Maintenance of internal environment e.g. aldosterone, parathyroid hormone, vitamin D 3. Energy production, utilisation and storage e.g. insulin, glucagon, thyroid hormones, cortisol, growth hormone

Topic 4: Cell to Cell

Ligands and receptors  Ligand is a signalling molecule that binds to a receptor  There are many different types of ligands in the body and receptors are highly specific for each ligand  This allows hormones to target organs or tissues expressing specific receptors  Signalling = cellular decision making in response to external stimuli  Signals lead to cell response, such as secrete, contract, move, divide, die, catabolise etc Water-soluble hormones  Peptide hormones cannot cross membranes, instead they require transmembrane receptors  Receptor then transduces the signal Second messengers  Molecules whose presence is a signal  Acts as amplifiers  Synthesised or released from storage  Act as intracellular ligands  Made or released by effector proteins

What’s needed for second messengers:  Low amounts in resting state  Regulated synthesis  Regulated destruction  Act through other proteins Steroid hormone

cAMP as a second messenger  G proteins bind to GTP  G protein-coupled receptor activated  G protein mobilised  G protein activates Adenylyl Cyclase  cAMP is produced from ATP and then activates kinases

Calcium as a second messenger  Calcium has profound effects on protein activity, interactions and conformation  Activation of membrane receptors  Calcium floods cells very quickly and changes cellular actions at all levels

Topic 5: Learning objectives

Learning objectives  Explain negative and positive feedback with physiological examples  Describe an example of homeostasis  Describe how sensors and feedback systems operate to maintain homeostasis in negative feedback loops  Explain the basis of how the body regulates extracellular fluid osmolarity  Explain how oxytocin and ADH work

Topic 5: Cell control

Major concepts  Maintaining stability in the body  positive and negative feedback loops  Cells/tissues/organs communicate with themselves and the outside world: Stimulus  sensor  control  effect Negative feedback loops  Homeostasis = maintenance of internal consistency  The tendency to counteract change from “set points” back to equilibrium o e.g. body temperature, blood glucose Positive feedback loops  Amplify initial stimuli to move system further away from its starting point o e.g. childbirth, blood clotting Pituitary gland hormones  The posterior pituitary secretes two main hormones: oxytocin and ADH (antiduretic hormone/vasopressin)  Oxytocin is responsible for uterine contractions and breast milk ejection  ADH is released in response to rise in osmolarity in blood, fall in blood pressure, fall in blood volume – to prevent water loss in kidneys through diuresis (increase in urine)

Topic 6 & 7: Homeostasis and Hormonal Regulation Topic 6: Learning objectives

Learning objectives  Identify that blood sugar level can be maintained by a negative feedback loop  Describe the mechanisms that maintain blood sugar in the fed state  Describe the mechanisms that maintain blood sugar during fasting

Topic 6: Homeostasis

Importance of glucose circulation  Brain is very dependent on blood glucose levels  It is the main source of energy for the brain  The brain does not store much glucose as glycogen i.e. glycogen levels are very low in the brain  Brain is only reliant on blood glucose, neurons in brain are not good at using other fuels Blood glucose set point = 5 millimolar Diffusive process of glucose around body  When we eat, glucose is present in high concentration in gut  moves from gut into bloodstream  high concentration in bloodstream  moves into muscle, fat and liver cells o After we eat a meal, glucose levels in the blood go up but then they reach a point where they don’t go any higher because excess glucose can be stored in sinks so over time, they level out 

When we don’t eat, glucose is present in high concentration in cells and low concentration in the blood  moves from cells into blood o When we don’t eat, glucose levels go down in the blood but are damped by the diffusive process of glucose as cells give up glucose to the blood, maintaining elevated blood glucose for a period of time

How glucose enters cells  Glucose cannot pass through cell membranes, so it requires transports (helps with passive diffusion, not active transport)  Transporters which help glucose cross membranes: SGLT and GLUT o SLGT needed in small intestine (transfer glucose from gut into blood) and kidney (recover glucose back into the blood) o GLUT4 needed for glucose uptake in muscle and fat and GLUT2 for liver

Topic 6: Homeostasis

Diffusion alone is not sufficient control of glucose  If we just allowed diffusive processes to occur, then blood glucose concentrations would go too low and too high  If blood glucose is too low, it would starve cells of energy and especially impact our brain function  If blood glucose is too high, over time it would cause damage to vasculature, nerve damage and kidney failure

Mechanism of storage or release  Diffusion is fundamental mechanism that enables glucose to be distributed across body, but we need another mechanism of storage and release to properly control glucose levels

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When blood glucose is too high, it is stored in the liver as glycogen. When blood glucose is too low, it is released from glycogen stores in the liver.

Muscle cells and glucose  STORAGE: o Glucose enters through GLUT4 transporters, metabolised into pyruvate and then into glycogen o Once converted into glycogen, cellular glucose concentration falls so the cell can take in even more glucose  RELEASE: o Glycogen stores are turned back into pyruvate and then out of the cell through aerobic or anaerobic exercise o If extreme fast, muscle can be digested as amino acids and used as energy

Topic 6: Homeostasis

Fat cells and glucose  STORAGE: o Glucose enters through GLUT4 transporters, metabolism leads to glycerol 3phosphate which is combined with fatty acids to form triglycerides o Fat cells have large capacity to store triglycerides so can uptake large quantities of glucose  RELEASE: o Triglycerides are turned into both fatty acids and glycerol which both enter blood circulation and are targeted by liver Liver cells and glucose  STORAGE: o Glucose enters through GLUT2 transporters, metabolised into glycogen  RELEASE: o Liver can reverse this process and covert glycogen into glucose and exits liver into bloodstream through same GLUT2 transporter o However, GLUT2 transporter  Liver uses amino acids and lactate from muscle cells  converted into pyruvate and used to make glucose  Liver uses glycerol from fat cells  converted into pyruvate and used to make glucose  Liver uses fatty acids from fat cells  converted into ketones (a fuel that can be used by the brain)

How the mechanisms of storage and release are controlled: The role of hormones  The storage of glucose is controlled by insulin released by pancreas  The release of glucose is controlled by glucagon released by pancreas

Topic 6: Homeostasis

Insulin and glucagon  MUSCLE CELL: o Insulin acts on the transporters in muscle cell  It leads to insertion or removal of GLUT4 transporters in membrane o In fasting state (no insulin)  no transporters in membrane o In fed state (insulin present)  increase in number of transporters in membrane  FAT CELL: o Same as muscle cell!  LIVER CELL: o GLUT2 transporter is regulated differently (not inserted or taken away), instead it is present all the time  Needs to be there all the time because it regulates glucose in AND out o Instead, insulin accelerates the processes of conversion of glucose to glycogen storage and glucagon accelerates the process of the breakdown of glycogen into glucose Cell

Insulin

Muscle

Promotes glucose uptake

Fat

Promotes glucose uptake

Liver

Promotes glycogen storage

Glucagon

Promotes glycogen breakdown and glucose release

Topic 7: Learning Objectives

Learning objectives  Describe the mechanisms that regulate insulin secretion in the pancreas  Outline the disease of diabetes and understand the differences between Type I and Type II diabetes

Topic 7: Hormonal Regulation

Pancreas cells responsible for insulin secretion  Pancreas is mostly exocrine tissue, responsible for excretion of digestive enzymes  However, throughout pancreas there is around 3 million islets of Langerhans  An Islet of Langerhans is approximately 200 microns in diameter and contains a few hundred to thousand cells and different cell types in each

 

Beta cells secrete insulin Alpha cells secrete glucagon

Control of beta cell release of insulin  The beta cell in the pancreas responds to glucose levels, amino acids and some hormones e.g. GLP-1 to stimulate the release of insulin

Topic 7: Hormonal Regulation

Process of beta cell function  High glucose concentration in blood  glucose enters cell through diffusion across GLUT2 membrane into the beta cell  Glucose is metabolised  ATP is generated  Increase in ATP levels in cell is recognised by receptor called K ATP-channel o If ATP is too high  potassium channel shuts causing depolarisation of membrane  Depolarisation triggers opening of VDCC (voltage gated calcium channel) so that calcium flows into cell  Elevation of calcium in cell triggers fusion of insulin containing granules with the cell membrane (exocytosis)

When blood glucose concentrations are low, not much glucose enters the cell. This means that the level of metabolism in the cell is low and there is not much ATP being produced. As a result, the potassium KATP-channels remain open and the cell membrane is hyperpolarised, instead of depolarised. This prevents the inflow of calcium through the voltage gated calcium channels and insulin is not released. Type I and Type II Diabetes

Type I Diabetes

Type II Diabetes

Symptoms

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Weight loss, fatigue, frequent urination, excessive thirst

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Slow healing of wounds, blurred vision, constant hunger, frequent urination, numbness of hands and feet, unexplained weight loss

Causes

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Autoimmune disease – antibodies present & used to diagnose Beta cells in Islets of Langerhans are damaged or destructed Number of beta cells declines until there aren’t enough to produce enough insulin

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Lifestyle disease – no antibodies present High sugar diet and no exercise, obesity Failure of beta cells to produce enough insulin – loss of first phase response to increase in glucose

Glucose testing throughout the day by finger prick or patch worn Insulin injections to bring blood glucose back to normal level

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Treatment

 

 

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Byetta injection which is a GLP-1 agonist (chemical that binds to receptor and activates receptor to produce response) Diet and exercise control

Topic 8 & 9: Excretion and Detoxification Topic 8: Learning objectives       

Topic 8: Excretion

Describe the anatomy of the kidney, the structure of the nephron and name and describe the structure and function of regions of the nephro...