IB Biology Option D - Human Physiology

Essential Nutrients

• Chemical substances found in foods used in the human body

• cannot be synthesized in the body and do not have a replacement made in the body

  • so must be ingestred

6 Classes of nutrients

• carbs

• proteins

• lipids

• vitamins

• minerals

• water

Malnutrition

• health condition caused by an imbalance or XS of nutrients in the diet

• Caused by improper dietary intake or inadequate use of nutrients by the body due to a disease/condition

Method of determining energy content of food

• Using calorimetry - Combustion

• Food is combusted in calorimeter, heat given off measured

• q=mcΔT

Comparison of energy content between carbs, lipids, and proteins

• Protein: Lowest relative energy content; protein metabolism produces nitrogenous waste products which must be removed from cells

• Carbs: Intermediate relative energy content; preferentially used as an energy source because it is easier to digest and transport

• Lipids: Highest relative energy content; stores more energy per gram but harder to digest and transport

Essential amino acids

• cannot be produced by the body, must be ingested

• eg. methianine

Non-essential amino acids

• can be produced in the body

• eg. alanine

Conditionally non-essential amino acids

• Can be produced but at lower rates than needed in certain conditions eg pregnancy or infancy

• Meaning they can be essential

• eg. glycine

PKU Causes

• Phenylketonuria: genetic condition that results in the impaired metabolism of phenylalanine

• autosomal recessive condition caused by a mutation which alters phenylalanine hydroxylase (PAH)

PKU Consequences

• Phenylketonuria: PAH (phenylalanine hydroxylase) can no longer convert excess phenylalanine to tyrosine, instead it is converted to phenylpyruvate (aka phenylketone)

  • build up of phenylketone in blood and urine may lead to brain damage and mental delays

Protein deficiency malnutrition

• shortage of one or more amino acids in diet will prevent the production of specific proteins

• health affects vary depending on the shortage

Treatment of PKU

• enforcing strict diet that restricts phenylalanine intake

• low protein diet with supplemented medical formal with precise amino acid content

Essential fatty acids

• polyunsaturated fatty acids necessary for health

• cannot be synthesized by humans

• consist of either omega-3 fatty acids or omega-6 fatty acids

• found in fish, leafy vegetables, walnuts

• eg. Alpha-linolenic acid (omega-3) and linoleic acid (omega-6)

• Modified in the body to make lipid-based compounds

Deficiencies of alpha-linolenic acid and linoleic acid linked to…

• impaired brain development (depression)

• altered maintenance of cardiac tissue (abnormal heart function)

Lipoproteins

since fats and cholesterols are hydrophobic, they must be packaged with proteins to be transported

Vitamins

• organic molecules with diverse and complex chemical structures

• may be water-soluble or fat-soluble

Water-soluble vitamins

• need to be constantly consumed since an excess is lost in urine

• eg. B and C

Fat-soluble vitamins

can be stored within the body, eg. A, D, E, K

Production of ascorbic acid

although many organisms can produce ascorbic acid (vitamin C), humans cannot, so it is considered essential

Scurvy symptoms

• anaemia

• dental issues

• hemmorhagin

• skin bruising and discoloration

Vitamin D production

• can be naturally synthesized in humans when a chemical precursor is exposed to UV

• hence vitamin D deficiency is usually seen in individuals without access to sunlight

Vitamin D function

• involved in the absorption of phosphorous and calcium by the body, which is essential to bone mineralization

Vitamin D deficiency

• can lead to deformed bones (rickets, children) or softened bones (osteomalacia, adults)

• Source = oily fish

Dietary minerals

chemical elements required as essential nutrients that must be consumed by organisms

Examples of minerals in human development

• Fe/P/Mg are major components of hard sturctures (bones, teeth)

• Na/K/Cl are components of body fluids

• Fe/P/I are cofoactores for specific enzymes and components of proteins and hormones

Examples of minerals in plant development

• Mg is an important component of chlorophyll

• K helps stoma open/close, helps diffuse H₂O into roots

• Ca is used for plant root and shoot elongation

Release of dietary hormones can be triggered by… (3 things)

• stretch receptors in the stomach and intestines during digestion

• adipose tissue releasing hormones in response to fat storage

• pancreas releasing hormones in response to changes in blood sugar concentrations

Clinical obesity

• Describes a significant excess in body fat

• caused by a combination of high energy intake and low energy expendature

Starvation

• describes the severe restriction of daily energy intake, leading to significant loss of weight

• may manifest in anorexia nervosa

Hypertension

• abnormally high blood pressure, which can lead to heart disease

• common in overweight individuals; excess weigh buts more strain on the heart

• high dietary cholesterol also increases blood pressure, and puts stress on the heart

Myocardial atrophy in anorexia

• in severe anorexia, the body begins to break down heart muscle, making heart disease the most common cause of death

• the heart tissue can starve and lose volume

• can also cause dangerous arrythmias

RDI

• Recommended daily intake

• Daily dietary level needed to meet requirements of health

• An estimation that varies according to age, gender, activity, medical conditions

• Based on a daily energy intake of 8400 kJ for healthy adults

• presented on food packages as a percentage of a daily total

• Dietary intake can be compared to one’s energy expenditure to monitor weight change

Exocrine glands

Produce and secrete substances via a duct onto the epithelial surface

Salivary glands secrete…

salivary amylase

Gastric glands secrete…

HCL, proteases

Pancreatic glands secrete…

Pancreatic juices with enzymes

Intestinal glands secrete…

Intestinal juices via crypts of Lieberkuhn

Gastric secretions controlled by…

nervous or hormone mechanisms; control volume and contents of secretions

Nervous control over gastric secretions

• sight and smell of food —> gastric juice secreted by stomach pre-ingestion

• Food enters stomach —> distension (swelling) is detected by stretch receptors in stomach lining, signals then sent to brain to trigger release of digestive hormones to achieve sustained gastric stimulation

• Brain sends signal to stomach via VAGUS nerve

Hormonal control over gastric secretions

• Brain sends signal via vagus nerve to endocrine cells to secrete gastrin

• Gastrin - secreted into bloodstreams from gastric pits of stomach to stimulate the release of stomach acids

  • If pH gets too low, gastrin secretion is inhibited by gut hormones (secretin, somatostatin)

• Duodenum releases digestive hormones when chyme enters small intestine

  • Secretin, CCK: both stimulate pancreas and liver to release digestive juices; pancreatic juices contain bicarbonate ions which neutralise stomach acids, liver produces bile for fat emulsification

Stomach acid secretion

• gastric glands lining stomach secretes acidic solution — optimum pH for hydrolisis rxns

Stomach acid functions

• assists in digestion by dissolving chemical bonds in food

• Activates stomach proteases — pepsin is activated when pepsinogen is proteolytically cleaved in acidic conditions

• Prevents pathogenic infection

Mechanisms of protection from low pH stomach acid

• mucus lines the stomach and protects the tissue from stomach acid

• bicarbonate ions from the pancreas released into the duodenum neutralises

• PPIs

Cons of antacids

• may impair digestion, leads to a higher chance of infection

Proton pump inhibitors

• reduces stomach acid secretion

• proton pumps in parietal cells of gastric pits secrete H⁺ via active transport, combined with Cl^- to form HCL (lower pH)

• PPIs irreversibly bind to proton pumps, preventing H⁺ release

  • raises pH to prevent gastric discomfort caused by high acidity, but may also increase susceptibility to gastric infections

Villus epithelial cells can be identified by…

• tight junctions - allows for concentration gradient

• microvilli

• many mitochondria (ATP for active transport)

• pinocytotic vesicles — materials ingested by breaking and reforming membrane

Dietary fibre

• indigestible portions of food derived principally from plants and fungi (cellulose and chitin)

• Humans lack cellulase , nut some ruminants have bacteria which aid in breakdown of indigestible plant matter in the digestive tract

Dietary fibre functions/benefits

• The rate of transmit of materials through large intestine is positively correlated with fibre content

  • provides bulk in intestines

  • absorbs water, which keeps bowel movements soft and easy to pass

Cardiac muscle cells stucture and function

• Branched; faster signal propagation and contraction in 3D

• Cells not fused, connected by gap junctions- communication between cells, at intercalated discs- holds cells together by adhesion; can contract independently while still being able to pass along electrical signals

• More mitochondria; more reliant on aerobic CR than skeletal muscle

Myogenic contraction

Cardiac muscle can contract without stimulation by CNS, contractions signalled by the SA/AV nodes

Unique functions of cardiac muscle

• longer contraction and refraction periods to maintain a viable heartbeat

• heart tissue not easily fatigued, contraction must my life long and continuous

• interconnected network of cells are separated b/n atria and ventricles to enable separate contractions

Autorhythmic cells

control coordinated contraction of cardiac muscle

SA nodes coordination of atrial systole

• collection of cardiomyocytes in right atrium

• primary pacemaker, controls rate of heartbeat

• sends electrical signals propagated through atria via gap junctions and intercalated discs

  • therefore atria wall cardiac muscles contract simultaneously in atrial systole

Atria and ventricles are seperated by…

fibrous cardiac skeleton composed of connective tissue; anchors heart valves in place, cannot conduct electrical signals

AV node

• located in cardiac skeleton in septum

• separates atrial and ventricular contractions

• propagates electrical signal after SA node relays it, but more slowly, hence delay

Electrical signal propagation in the heart

• SA node = primary pacemaker

• Transmits signal via ap junctions to atrial myocardium; atria contracts

• Signal received by AV node, then sent down septum via the bundle of His

• innervates the Purkinje fibres in ventricular walls — contraction

Bundle of His

specialized bundle of cardiomyocytes in septum

Significance of ventricular contraction beginning at the apex

by initiating ventricular contraction with the Purkinje fibres at the bottom of the ventricle first, ensure blood is forced upwards out the arteries

Diastole relative length and function

• relatively long period of insensitivity

• allows the atria to fill with blood and prevents fatigue of heart tissue

purpose of heart valves

• prevent backflow

• ensuring one-way circulation

Heart beat sounds

• 1st: closure of atrioventricular valves at the start of ventricular systole

• 2nd: closure of semilunar valves at the start of ventricular diastole

Electrocardiography

• can map cardiac cycle (periods of systole and diastole) by generating an electrocardiogram

Electrocardiogram: P wave

depolarisation of atria in response to signalling from SA node (ie. contraction of atria)

Electrocardiogram: QRS complex

depolarisation of ventricles (ie. contraction of ventricles triggered by AV node)

Electrocardiogram: T wave

repolarisation of ventricles - ventricular relaxation - completion of a standard heart beat

Electrocardiogram: PR interval, ST segment

inactive periods to allow blood flow

Cardiac output

• describes the amount of blood the heart pumps through the circulatory system in one minute (mL/min)

• Medical indicator of how efficiently the heart can meet the body’s demands

Cardiac output equation

CO (mL/min) = Heart rate (beats/min) x stroke volume (mL/beat)

Heart rate

• the speed the heard beats, contractions/min or bpm

• each ventricular contraction forces a wave of blood through the arteries = pulse

• normal = 60-100 bpm

Factors affecting heart rate

• exercise

• age

• disease

• temperature

• emotional state

Stroke volume

• blood pumped to body with each beat of the heart

• affected by the volume of blood in the body, contractility of the heart, resistance from blood vessels

• changes in SV affect BP, more blood or more resistance causes higher BP

Hypertension causes and consequences

• abnormally high blood pressure; either systolic or diastolic or both (greater than 140/90)

• causes: sedentary lifestyle, salt and fatty diets, excessive alcohol or tobacco use, may be secondary to other conditions, caused by medications

• hypertension does not cause symptoms but leads to consequences in long term due to narrowing of blood vessels

Thrombosis causes and consequences

• clot formation within blood vessels

• cholesterol deposits damage artery vessels

• atheromas (fat deposits) reduce lumen diameter, high blood pressure damages walls, forming atherosclerotic plaque/inelastic scar tissue

• if the plaque ruptures, a clot (thrombus) forms

• if embolus travels to brain → stroke

• if clot in coronary arteries → myocardial infarction

• high cholesterol, saturated, trans fat diets as a cause

CHD

• coronary heart disease, caused by build-up of plaque in coronary arteries

• Risk factors: age, diet, obesity

Fibrillation

• rapid irregular unsynchronised contraction of heart muscle fibres results in suboptimal blood flow

• The defibrillator applies a controlled electrical current to the heart, depolarizing heart tissue to terminate unsynchronized contractions, normal heart beat should then be re-established by the SA node

Artificial pacemaker

• delivers electrical impulses to heart to regulate the heartbeat

• highly programmable, adjustments can be made as required,

• treats abnormally slow heart rate - bradycardia

• treats arrhythmias arising from blockages in hearts electrical conduction system

Hormone

• signalling molecule produced by glands and transported to target cells via blood vessels

• recognizes specific protein binding sites to cause various responses

Hypothalamus function

• maintains homeostasis by linking nervous and endocrine systems

Pituitary gland structure and function

• adjacent to hypothalamus and in contact with it via portal blood system

• 2 lobes

• “master gland”

Anterior lobe

• hypothalamus produces releasing factor proteins, released into portal vessels by

  neurosecretory cells

• Cause endocrine cells in the anterior

  pituitary to release specific hormones into

  the bloodstream

Posterior lobe

• Hypothalamus produces hormones which enters a neurosecretory cell which extends through the posterior lobe to be released into the blood

Exocrine glands vs endocrine glands

• Exocrine secretes substances into ducts, leading to the epithelial surface

• Endocrine = ductless (Secretes hormones directly into the blood system)

Steroid hormones key features

• lipophilic, can diffuse across the plasma membrane

• binds to a protein receptor in the cytoplasm or nucleus

• receptor-hormone complex acts directly on DNA as a transcription factor controlling gene expression

Steroid hormones examples

estrogen, progesterone, testosterone

Peptide hormones key features

• hydrophilic so cannot diffuse across the plasma membrane

• bind to protein receptors on membrane surface which are coupled to internally anchored proteins

• activates second messengers (eg. cAMP, Ca²⁺, etc.) to allow for signal transduction—amplification of original signal

Peptide hormones examples

Insulin, glucagon, leptin, ADH, oxytocin

Somatotropin

• growth hormone, anabolic peptide hormone

• secreted by anterior pituitary

• reduces adipose tissue

• indirectly increases muscle mass, and bone size, by promoting IGF (insulin growth factor) produced by the liver

• Promotes growth and regeneration, performance enhancer

Oxytocin

• produced by hypothalamus, secreted by neurosecretory cells extending through posterior lobe

• release triggered by stimulation of sensory receptors in breast tissue

• positive feedback loop results in continuous secretion of oxytocin till infant stops feeding

Prolactin

• secreted by anterior pituitary in response to release of prolactin release hormone (PRH)

• inhibited by progesterone (preventing milk production before birth)

• involved in production of milk

Lactation

production and secretion of milk my maternal mammary glands following birth (controlled by prolactin and oxytocin)

Haemoglobin composition

• four polypeptides

• four haem groups, each with a Fe

  • hence can rxt with 4 O₂

Haemoglobin cooperative bonding

• changes shape and affinity when carrying O₂

  • proteins can undergo conformational changes to perform function

• changes shape so affinity for O₂ increases until saturation

  • it has a progressively higher O₂ affinity as more oxygens bind on

• no affinity with 4 O₂

Oxygen dissociation curve description

• plots oxygen partial pressure (mmHg) against oxygen saturation of haemoglobin or myoglobin

• S-shaped/sigmoidal graph

• low affinity (% saturation) for O₂ at low pressures of oxygen, higher affinity at higher pressures of oxygen

Myoglobin composition and function

• O₂ binding protein in skeletal muscles

• composed of one polypeptide, with one haem group, that can bind to one O₂

  • Therefore not capable of cooperative binding

• Has a higher affinity for O₂ and becomes saturated at lower partial pressures of oxygen

• holds onto oxygen supply until levels in muscles are very low to prevent onset of anaerobic cellular respiration (last reservoir)

Myoglobin oxygen dissociation curve

• logarithmic shape

• higher saturation than haemoglobin at any given partial pressure of oxygen

Fetal haemoglobin vs adult haemoglobin

• Fetal haemoglobin is structurally different than adult haemoglobin

• has a higher affinity for O₂ so its oxygen dissociation curve is shifted left — at any given O₂ partial pressure it will be more saturated than adult haemoglobin

• means it will load O₂ when adult haemoglobin is unloading in placenta capillaries

• adult haemoglobin almost completely replaces fetal after birth

Bohr shift

• High levels of dissolved CO₂ lowers pH of blood (H₂CO₃), which alters haemoglobins uptake and release of O₂

• Causes it to release O₂ shifting the dissociation curve to the right

• promotes oxygen release at regions of greatest need (with high metabolism/CR/CO₂ production)

CO₂ possible forms of blood transport

• small percent remains dissolved in blood (toxic in high concentrations though)

• some CO₂ enters RBCs, reversible bound to haemoglobin

• 70% majority converted to hydrogen carbonate ions (HCO₃^-) in RBCs

CO₂ conversion to HCO₃^-

CO₂ + H₂O → H₂CO₃ → HCO₃^- + H⁺

Carbonic anhydrase Spontaneous dissociation

Chloride shift

• for every HCO₃^- that exits a specialised protein channels, one Cl^- enters the RBC to maintain charge in the cell