BIO1008 Final notes PDF

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BasicsHomeostasisThe process by which organisms maintain a relatively stable internal environment - Strict confermer → changes internal to suit environment conditions (humans) - Endothermic Homeotherms - Strict regulator → maintains internal conditions - ectothermic poikilothermsExample: Heat The ho...

Description

Basics Homeostasis The process by which organisms maintain a relatively stable internal environment - Strict confermer → changes internal to suit environment conditions (humans) - Endothermic Homeotherms - Strict regulator → maintains internal conditions - ectothermic poikilotherms

Example: Heat The hometherm needs a much higher energy investment to maintain ideal core body temperature than a poikilotherm, but comparatively homeotherms can only function over a very narrow range of body temperature Behavioural - Avoidance - Hudduling - torpor/hibernation

Physiological - Insulation - Countercurrent exchange - Heat shock proteins (HSPs) and antifreeze proteins - Vasodilation/vasoconstriction - Variable metabolic rate - Non-shivering thermogenesis

Countercurrent exchange Heat exchange pampiniform plexus - Warmer blood in arteries are place next to the - The heat of testes needs to be cooler than the veins with colder blood, to warm them (often core body temperature in extremities)

Communication

Feedback loops - A mechanism in the body that tends to counteract the stimulus, so that balance is maintained Negative feedback loops A self-regulation mechanism in which the body responds to and counteracts a stimulus to maintain optimal conditions for the body maintaining homeostasis. Positive feedback loop A mechanism in which the stimulus is enhanced or accelerated to achieve some means and continues to do so until a negative feedback loop is activated by the body. Example Heat: Labour contractions - Positive feedback mechanism Stimulus - The first contractions of labor push the fetus against the cervix Receptor - The Cervix contains stretch-sensitive nerve cells that monitor the degree of stretching - These nerve cells send a message to the pituitary Control centre - The pituitary gland which secretes oxytocin Effector - Oxytocin causes stronger contractions of the smooth muscles in of the uterus pushing the baby down the birth canal When the cervix is no longer being stretched the body will signal the stopping of the release of oxytocin.

Temperature - Negative Feedback mechanism - 36.1 to 37.8 degrees Receptor: - Peripheral receptors are located in skin - Central thermoreceptors monitor the temperature of the blood as it passes through the brain - hypothalamus Control center: - hypothalamus can detect small changes in temperature (fractions of a degree) Responses: Hypothalamus → decrease in temperature - Motor neuron → making muscles under skin to cause shivering → generating heat - Vasoconstriction → Motor Neuron → blood vessels near skin constrict → divert warm blood away, minimising loss of

Blood clotting - Positive feedback loop

heat from skin Hormone → Thyroid gland releases thyroxine → increases metabolic rate Hypothalamus → Increase in temperature -

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Vasodilation → Skin Blood vessels → dilate → flush capillaries with warm blood → heat radiates from skin surface Sweat glands activated → secrete perspiration that is evaporated by body heat → cooling down body

Communication - Individuals cells communicate so that we live as a well integrated whole. - The quality of communication depends on; - The production of the signal - Transmission and modulation of the signal - Reception of the signal by targeted cell

Hormones

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Nervous system Organisations - central nervous system (CNS) - the brain and spinal cord - Peripheral nervous system (PNS) Peripheral nerves carry messages to the CNS through ‘electrochemical impulses - All other nerves Neurons Structure

Controlled by positive and negative feed back loops

Major sites - The brain: particular hypothalamus, pituitary gland and pineal gland - Throat: Thyroid and parathyroid glands are located - thymus ; Produced hormones important in immunity - Adrenal gland; located on kidney - Pancreas; pancreas islets regulate blood and sugar levels - Gonads: on female ovaries and male testes The functioning - Hormones produced have specific receptors

Function: - Sensory input: COnduction of signals from sensory receptors → integration centers -

Integration: Information from sensory receptors is interpreted and associated with appropriate responses of the body

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Motor output: Conduction of signals from the processing center → effector cells that actually carry out the body’s response (muscle and

gland cells)

Hormones; - Water-soluble - Travel freely in blood - Receptors are found on the surface of the plasma membrane of the target cell → These would be coupled to other cellular systems which mediate the action of the hormone inside target cell (signal transduction pathway) - Lipid soluble - Bind to transport proteins to travel in blood - Receptors of target cell reside in its nucleus and sometimes its cytoplasm → this is because hormones can diffuse through its phospholipid bi layer of the

Communication: - Happens between neurons at the synapses - Tiny gap between a synaptic terminal of an axon and the receiving portion of another neuron or effector cell - A nerve impulse traveling from one neuron to another across a gap between the axon terminal of one neuron and the dendrite → Gap is called synapse - Electrical impulse traveling down an axon will initiate a release of a chemical called a neurotransmitter - These neuro transmitters travel across synapses to the dendrites of another neuron

cell membrane Transport molecules - Transport but also regulate the activity of hormones - Mopping up excess production - Transport more than one hormone - Increase the biological potency compared with a hormone that is not bound to a transport molecule Hypothalamus Posterior pituitary - Extension of the hypothalamus - Oxytocin → incuse uterine contractions and milk ejection - Antidiuretic hormone → enhances water absorption in kidney Anterior pituary Thyrotropin GOnadotropin Growth hormone Cortiotropin

Autonomic nervous system - Parasympathetic division - Rest and digest - Sympathetic division - Fight or flight - Enteric division - regulates the movement of water and electrolytes Reflex Arc - Quick reactions that bypass the brain - Synapses at spinal cord without the delay of passing signals through the brain

Reproduction Basics Asexual repoduction Reproduction that involves a single organisms to create offspring that is genetically identical to its parent - ie., Binary fission → the separation into two binary or more individuals of about equal size → Mostly found in unicellular organisms BUT can also be found in multicellular organisms such as sea anemone - Ie., Budding → creating new individuals - Ie., Parthenogenesis → eggs develop into new individual without fertilisation ie., bees - Fertilised = female (2n) → - Unfertilised = male (1n) → despite being haploid will function normally - E.g., Female komodo dragon (sungai)

Sexual reproduction reproduction that brings the genes of two parent individuals together, generating a new individual - Genes from two parents mix - Fertilisation → fusion of gametes to form a diploid zygote - Male gamete = sperm (smaller and mobile) - Female Gamete = ovum - Germ cells = cells that produce gametes

Fertilisation External Fertilisation - a male organism’s sperm fertilizing a female organism’s egg outside of the female’s body (advantages)

Internal fertilisation - the union of an egg cell with a sperm during sexual reproduction inside the body of a parent. (advantages)

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External fertilization in an aquatic environment protects the eggs from drying out. - Broadcast spawning can result in a greater mixture of the genes within a group, leading to higher genetic diversity and a greater chance of species survival in a hostile environment (disadvantages) - Lower rates of fertilisation - Stricter conditions needed ie., temperature, moisture - The survival rate of eggs produced through broadcast spawning is low.

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Protects the fertilized egg from dehydration on land. - The embryo is isolated within the female, which limits predation on the young Disadvantages - Fewer offspring produced

Sex Note on ‘Two fold cost of sex’ → ? mentioned in lecture Females contribute the resources to foetus but only ½ the genes, males contribute 1.2 the genes but no resources. - Hence, females are contributing much more: How does this evolutionarily make sense? - ‘An asexual female would be able to transmit twice as many genes for the same ‘price’ per offspring → considering we survive to pass on as many genes as possible to the next generation 1. Recombination scrambles genotypes → can disrupt favourably adapted gene combination 2. Asexual repoduction can preserve genotypes and is more efficent than finding mates - Meiosis and reproduction, takes much longer than mitosis ie.. binary fission

Sex? What is Sex? - Chromosomal Makeup - XX or XY - Internal Organs - Testes or ovaries - External genitalia - penis or vagina Sex Chromosomes? - Males are Heterogametic → two differnt sex chromosomes - Females are homogametic → XX

Stages in reproductive development Pre-requisites for usual sex development 1. Formation of Urogenital Ridge (tissue that will - Intact chromosome complement develop into testes or ovaries) - Fully fucntioning sex determination genes 2. Gonad Formation - be testes or ovaries - Intact steroid hormone pathway determined by presense and activty of SRY - Default development option is female (sex determining reigion Y) gene - Splits from female to male at about six weeks 3. Sex determination - typically occurs as a consequence of gonad formation - In males the SRY gene will give instruction to gonads to turn into testes, which without instruction would have turned into ovaries 4. Sex differentation - recognizing how the sexes are phenotypically differntiated - Y chromosomes → Disorders Difference of sex development (DSD) → intersex

Androgen (testosterone) related

conditions - Turner syndrome - 45 X or XO (only effects females) - - 1 in 200 girls in australia - Monosomy (1X - Not inherited - SHOX gene (on X chromosome) → important for bone development and growth: if it us damaged or missing the result is short stature - Rarely fertile - Klinefelter Syndrome - 47 or XXY (only affects males) - 1 in 500/1000 brith in australia - Phenotypically men but an extra X chromosome - Low production of testosterone → feminizing influences - High chance of infertility

- Testosterone biosynthetic defects - 1:130,00 - Gonadal dysgenesis - 1:150,000 - Micro penis Androgen insensitivity syndrome 1: 13,000 → complete or partial testicular feminisation syndrome - Born with the XY chromosome → but did not develop into a male instead staying a female in early development - testosterone and dihydrotestosterone receptors ineffective in target or all cells → cannot bind to produce response → these protein receptors are - External genitalia is female - testes in abdomen little hair, well developed breasts - Gonads develop based on genetics (XY) - this is fixed development - But hormones act as modifying agents so we get the default female phenotype because the body cannot respond to the androgens secreted - Body is ‘blind’ to testosterone - Caused 5-alpha reductase deficiency - no estimate - Genetically male XY chromosomes - Caused by Lack of enzymes that converts testosterone to dihydrotestosterone - Testosterone masculinizes internal genitalia but development of penis and scrotum needs DHT - As puberty approaches a large surge of testosterone is released lead to further

development of penis and male phenotype development Congenital adrenal hyperplasia 1: 13,000 - Caused by mutation in genes that produce hormones progesterone to other hormones - Progesterone Hormone overflow is directed to androgen production = more testosterone - Females display masculinised genitals - Can be classed as an intersex disease

Puberty Transition from sexually immature child to secually mature adult Physiological Changes - Growth spurt - Morphological changes - Definitive signs - Girls - Menarche (first menstrual bleeding) - Boys - ejaculation (wet dreams) The activation of the hypothalamic-pituitary-Gonadal axis (HPG axis) Reference to hypothalamus, pituitary gland, and gonadal glands as if these individual endocrine glands were a single entity. - Three main axes - Hypothalamic pituitary thyroid axis (HPT) - Hypothalamic - pituitary adrenal axis

Hypothalamic - pituitary- gonadal axis (HPG) feedback loop This feedback loop plays a large role in regulating the production and release of hormone within the body to regulate reproduction - GnRH = gonadotropin releasing hormone - LH = Luteinizing Hormone - FSH = Follicle stimulating Hormone

(HPA)

Puberty Birth High levels of sex hormone in foetuses especially in males - From foetal secretion AND/OR can be transferred from mother to foetus - Someone babies can have breasts and breast milk - Then a decline until puberty Puberty

- When the HPG axis activates 1. Gonadotropin-releasing hormone (GnRH: a peptide hormone) from hypothalamus 2. Signal pituitary gland to release two other hormones a. Luteinizing hormone (LH) b. Follicle stimulating hormone (FSH) 3. These hormones stimulate the gonads (Ovary and testes to produce sex hormones) Hormones - Gonadotropin releasing hormone (GNRH) - Released in pulses from hypothalamus - Drives the pituitary release of LH and FSH → causing testes and ovaries to develop and adopt a primary role in reproduction as well as playing a critical role in the endocrine system Physiology of puberty - Activation of HPG axis - Induces and enhances the progressive ovarian and testicular sex hormone secretion - Is responsible for the biological, morphological and psychological changes to which the adolescent is subjected - Appearance and maintenance of secondary sexual characteristics - Produces and regulates capacity for reproduction Precocious puberty -

Increased body fat - Lead to hypothesis that human females should maintain adequate body fat to both commence menstruation and fertility → young females should not risk pregnancy in cause supplies of food dwindle - People are reaching the critical body weight earlier hence menstruation is starting again

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Amenorrhea - Strenuous training and severe weight loss are associated with high instance of menstrual dysfunction - Delayed onset of menstruation When energy is plentiful, animals can afford to engage in optimal levels of all activities → but this is rare so animals are forced to set priorities - Reproduction is deferred → for greater

success of rearing offspring - Other energy expending activities are Environmental factors reduced → energy is rerouted to more - No evidence for hormonal growth promotes important activities inducing menstruation early - Effect - However as it is used in cattle to change - Leptin → hormone that signals to body the fat, muscle mass there is evidence how well ones fat cells are endowed to suggests that perhaps this maybe - If there is less released → the body stops also be affecting our fat etc levels → producing LH inducing earlier periods - Large incidence of precocious puberty in Puerto Rico in 1978-1981 - Probable oestrogenic contamination of food but no single cause identified - Extensive menarche and genomasticia Endocrine disruptors - Affecting the many stages of hormonal systems - Preventing synthesis of hormones - Directly binds to hormone receptors - Interfere with hormone → end up with Social factors higher concentrations of hormones - Over sexuality of popular media - Examples: - Family stress - DDT → pesticides (now banned) - Presence of parent figures - PCBs → can induce deformities - Crocs in florida - Diminutive phalli - Lower plasma testosterone and less aggressive - Dioxins - Humans effects - Declining sperm count - Congenital malformations

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Cancer → hormone related Disrupted sexual behaviour Disrupted neurobehavioral development

Male reproduction Structure - Divided into two components in testes - Spermatozoa → seminiferous tubules supported by sertoli cells → sperm in the fluid filled cavity of lumen - Hormones (androgens) are synthesised between seminiferous tubules in the leydig cells Function - Production of sperm (spermatogenesis) - Maturation of sperm (spermatogenesis) - Production of sex steriod hormones (androgens) - Delivery of Sperm from testes to receptor environment for fertilisation Development 1. At sex week the SRY gene is activated by Y chromosome and gonads to turn into testes 2. At puberty separation is affected by cellular barriers that limit exchange of substances a. Sertoli cells form tight junctions that further separate the tubular compartment creating a

Spermatogenesis 1. Pro-spermatogonial cells: quiescent till puberty 2. Mitosis: Morphologically distinct spermatogonia 3. Mitosis: Several times into primary spermatocytes 4. Occurs in basal parts of tube a. Duplicate DNA b. Push into adluminal (non-fluid) compartment - chemically distinct compartment 5. In adluminal compartment (non fluid lumen area) a. Meiosis I: haploid secondary spermatocytes b. Meiosis II: spermatids c. Four spermatids produced from each spermatocytes 6. Cytodifferentiation a. Conversion of simple round cell into the complex morphology of mature sperm

blood-testis barrier - Allows sperm to develop in a chemical environment different from blood and lymph - The separation of blood and sperm → stops things in blood affecting ones sperm ie., medication, alcohol, etc - Prevents sperm leaking out into blood/immune response that destroy the sperm What is sperm - Fluids from a variety of glands that feed into urethra - Seminal vesicles - Prostate gland - cowper’s gland - Each ejaculate (2-5 ml) contains: - Fructose sorbitol - Alkaline buffering agent - Reducing agents (oxidation - Prostaglandin (vaginal contractions)

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Cell elongates (propulsion) Midpiece - full of mitochondria energy Head (enzyme rich cap called acrosome that surrounds DNA which will contribute to fertilisation

7. Hormonal control is via testosterone produced by the leydig cells 8. Appropriate levels are maintained by an interaction between hypothalamic gonadotropin releasing hormone (GnRH), pituitary hormones, luteinizing hormone, FSH and inhibin from sertoli cells (when there full of sperm) 9. Epididymis and sperm maturation - Sperm washed away from sertoli cells by fluid - Transported through muscular action of epididymis - Secretes sugars and glycoprotein → transformation of tail and acrosome - Tail can now move - Maturation - 9 days - Storage 3 days → reabsorption or dribble into urethra

Feedback loop 1. Level of hypothalamus decreases 2. Hypothalamus is stimulated to secrete Gonadotropin releasing hormone 3. The GnRH hormones stimulates the anterior pituitary to secrete Luteinizing hormone and follicle stimulating hormones 4. The LH promotes testes to produce testosterone a. Elevated levels of testosterone inhibits secretion of GnRH 5. FSH and sertoli cells bind to produce testosterone AND spermatogenesis a. High sperm count induces sertoli cells to secrete inhibin 6. Testosterone stimulates formation and development of sperm 7. Level of testosterone decreases and hypothalamus secretes GnRH Erection - Result of nervous system action causing: - arterial blood flow (into the penis) → erection - Decreased venous flow (flow out of penis) - Testosterone is not necessary for all types of erections

Ejaculation - Muscular contracts expel semes to urthera - Muscular contractions of erectile tissue lead to ejaculation - Exactly what triggers it is unknown

Reproductive disorders

Impotence - Used to be thought it was psychogenic (performance anxiety); how many believed to be organic - Can affect - All ages - Vascular problems - Smokers, antagonistic drugs - Obstruction to flow cavern...