bio124 Flashcards
(232 cards)
1
Q
Signalling systems
A
Needed to coordinate activities of cells and tissues, regulate neurotransmission, control developmental processes, and maintain homeostasis.
2
Q
Three main types of signalling
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- Free diffusion (Autocrine, Paracrine, Endocrine), 2. Cytoplasmic connections, 3. Direct cell-to-cell contact.
3
Q
Autocrine signalling
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A type of cell signalling where a cell secretes chemicals that act on itself, often involved in growth regulation.
4
Q
Paracrine signalling
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Cells secrete chemical signals that affect nearby cells, typically playing a role in embryonic development.
5
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Endocrine signalling
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A type of long-distance signalling where hormones are secreted into the bloodstream to affect distant cells.
6
Q
Synaptic signalling
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A specific form of paracrine signalling where neurotransmitters pass signals between neurons or from neurons to muscle cells.
7
Q
Fastest mode of cell-to-cell communication
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Signalling via cytoplasmic connections, such as gap junctions in heart muscle cells.
8
Q
Ligand
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A molecule that binds to a receptor on a cell surface, triggering a signalling pathway.
9
Q
Two main types of signalling molecules
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- Local regulators (act on nearby cells, e.g., growth factors, prostaglandins, neurotransmitters), 2. Hormones (travel through the bloodstream to target distant cells).
10
Q
Nitric oxide (NO) as a signalling molecule
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Acts as a paracrine signal, inducing vasodilation in the cardiovascular system. It has a short half-life (1-5 seconds).
11
Q
Prostaglandins
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Modified fatty acids involved in various functions like inducing labor contractions and inflammation.
12
Q
Three main steps in a signal transduction pathway
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- Reception - Ligand binds to a receptor. 2. Transduction - Signal is relayed and amplified through multiple steps. 3. Response - The cell carries out a specific action.
13
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Signal amplification in transduction
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A few signal molecules can trigger a large cellular response through multiple steps, such as phosphorylation cascades.
14
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Different responses to the same signal
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Different cell types have different receptor proteins and intracellular signalling pathways, leading to varied responses.
15
Q
Homeostasis
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The maintenance of a stable internal environment through negative feedback loops, like blood glucose regulation.
16
Q
Three main stages of cell signaling
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- Reception - Detection of a signal molecule (ligand) by a receptor. 2. Transduction - Relay and amplification of the signal. 3. Response - Cellular activity triggered by the signal.
17
Q
Role of a ligand in cell signaling
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A ligand is a small molecule that binds to a receptor, triggering a conformational change that initiates a signal transduction pathway.
18
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Two main types of ligands based on solubility
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Hydrophilic ligands - Bind to membrane receptors as they cannot pass through the membrane. Hydrophobic ligands - Pass through the membrane and bind to intracellular receptors.
19
Q
Three main types of membrane receptors
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- G-protein-coupled receptors (GPCRs) 2. Receptor tyrosine kinases (RTKs) 3. Ion channel receptors
20
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G-protein-coupled receptors (GPCRs)
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The largest family of cell surface receptors that activate G proteins, which switch between active (GTP-bound) and inactive (GDP-bound) states.
21
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Activation of a G protein
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A ligand binds to a GPCR, causing a shape change that allows the receptor to interact with a G protein. GTP replaces GDP, activating the G protein.
22
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Inactivation of G proteins
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The G protein hydrolyzes GTP to GDP, returning to its inactive state and stopping the signal.
23
Q
Examples of pathways that use GPCRs
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- Epinephrine (Adrenaline) - Stimulates glycogen breakdown. Cholera & Whooping Cough - Disrupt GPCR function. Many medicines (60%) target GPCR pathways.
24
Q
Receptor tyrosine kinases (RTKs)
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RTKs are membrane receptors with intrinsic enzyme activity that phosphorylate tyrosine residues. They can trigger multiple signalling pathways and are often involved in cell growth and cancer.
25
Medical application of RTKs
Herceptin - A monoclonal antibody that inhibits HER2, a receptor tyrosine kinase involved in aggressive breast cancer.
26
Function of ligand-gated ion channels
They act as gates that open when a ligand binds, allowing ions (e.g., Na+, Ca2+) to enter or exit the cell, crucial in nerve signaling.
27
Examples of drugs that target ion channels
- Verapamil - Calcium channel blocker (for hypertension). Lidocaine - Sodium channel blocker (local anesthetic). Glipizide - Potassium channel blocker (for diabetes).
28
Intracellular receptors
Found in the cytoplasm or nucleus, they bind to small, hydrophobic ligands like steroid hormones and directly regulate gene transcription.
29
Testosterone action through intracellular receptors
Testosterone enters the cell, binds to its receptor, and forms a hormone-receptor complex that acts as a transcription factor, triggering protein synthesis.
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Components of a signal transduction pathway
Reception (signal binds to receptor), Transduction (signal relayed via molecular interactions), Response (cellular activity triggered).
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Benefits of multistep pathways in signal transduction
They amplify the signal, coordinate complex responses, and provide multiple regulatory points.
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Protein phosphorylation
It's the process where protein kinases transfer a phosphate group from ATP to a protein, often activating it.
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Role of protein phosphatases
They remove phosphate groups from proteins, acting as an off-switch in signal transduction.
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Phosphorylation cascade
Each activated protein kinase phosphorylates the next protein in a sequence, amplifying the signal.
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Second messengers
Small molecules like cAMP, Ca²⁺, and IP₃ that rapidly diffuse and help relay signals inside the cell.
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Enzyme converting ATP to cyclic AMP (cAMP)
Adenylyl cyclase, in response to extracellular signals.
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Cholera toxin effect on signal transduction
It locks a G protein in its active state, causing excessive cAMP production and leading to dehydration via ion loss.
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Importance of calcium (Ca²⁺) as a second messenger
Cells maintain low cytoplasmic Ca²⁺ levels, so its rapid increase can strongly affect cellular functions.
39
Inositol triphosphate (IP₃) in calcium signaling
IP₃ binds to calcium channels in the ER, triggering Ca²⁺ release into the cytosol.
40
Function of calmodulin (CaM) in calcium signaling
CaM binds Ca²⁺ and regulates kinases, phosphatases, and adenylyl cyclases.
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Key nuclear responses in signal transduction
Activation of transcription factors to regulate gene expression and enzyme production.
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Scaffolding proteins
They organize multiple relay proteins, increasing efficiency of signal transduction.
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Aspects of fine-tuning a signaling response
Amplification, specificity, efficiency (via scaffolding proteins), and termination of the signal.
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Termination of a signaling pathway
Ligand dissociation, receptor inactivation, phosphatases removing phosphates, and second messenger breakdown.
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Endocrine Glands
Glands that secrete hormones directly into blood.
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Hypothalamus
Key regulator of hormones, controls pituitary.
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Pituitary Gland
Divided into anterior and posterior sections.
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Tropic Hormones
Hormones that act on other endocrine glands.
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Trophic Hormones
Hormones that stimulate growth of tissues.
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Hypothalamo-Hypophyseal Portal System
Transports hormones from hypothalamus to anterior pituitary.
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Releasing Hormones (RH)
Hormones that stimulate release from anterior pituitary.
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Inhibiting Hormones (IH)
Hormones that inhibit release from anterior pituitary.
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Growth Hormone (GH)
Stimulates growth and metabolic functions.
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Insulin-like Growth Factors (IGFs)
Mediates growth effects of GH.
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Prolactin
Stimulates milk production in lactating women.
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Oxytocin
Stimulates uterine contractions and milk ejection.
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Anti-Diuretic Hormone (ADH)
Regulates water balance in the body.
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Feedback Mechanisms
Regulatory processes controlling hormone release.
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Hypersecretion
Excessive hormone production leading to disorders.
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Hyposecretion
Insufficient hormone production leading to disorders.
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Acromegaly
Excess GH in adults causing enlarged features.
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Gigantism
Excess GH in children causing excessive growth.
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Pituitary Dwarfism
Insufficient GH in children leading to stunted growth.
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Melanocyte Stimulating Hormone (MSH)
Regulates pigmentation and appetite.
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Adrenocorticotropic Hormone (ACTH)
Stimulates adrenal gland to release glucocorticoids.
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Corticotropin Releasing Hormone (CRH)
Stimulates release of ACTH from anterior pituitary.
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Neurohypophysis
Posterior pituitary, stores hormones from hypothalamus.
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Adenohypophysis
Anterior pituitary, synthesizes and releases hormones.
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Ghrelin
Hormone that stimulates appetite from stomach.
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Feedback Loop
Process where hormone release affects further release.
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Sympathetic Control
Nervous system control over adrenal gland functions.
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Hypothalamic-Hypophyseal Tract
Neural pathway connecting hypothalamus to posterior pituitary.
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Thyroid Gland
Lobular structure joined by an isthmus.
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Follicular Cells
Secrete thyroxin (T3 and T4) hormones.
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Parafollicular Cells
Secrete calcitonin to regulate calcium.
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Thyroglobulin
Colloid in follicles, precursor for thyroid hormones.
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Thyroxin (T4)
Less active thyroid hormone, converted to T3.
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Triiodothyronine (T3)
Active thyroid hormone with three iodine atoms.
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Iodine Trapping
Follicular cells transport iodide from blood.
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Negative Feedback Control
Regulates stable levels of thyroid hormones.
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Hypothyroidism
Condition with low thyroid hormone levels.
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Hyperthyroidism
Condition with excessive thyroid hormone levels.
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Calcitonin
Lowers blood calcium levels, promotes bone density.
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Parathyroid Gland
Secretes parathyroid hormone (PTH) for calcium regulation.
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Chief Cells
Secrete parathyroid hormone (PTH) in parathyroid gland.
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PTH Actions
Increases blood calcium by promoting bone resorption.
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Calcitriol
Active vitamin D, increases calcium absorption.
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Adrenal Gland
Located above kidneys, divided into cortex and medulla.
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Zona Glomerulosa
Secretes mineralocorticoids like aldosterone.
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Aldosterone
Regulates sodium and potassium homeostasis.
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Renin-Angiotensin-Aldosterone System
Controls aldosterone secretion pathway.
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Glucocorticoids
Regulate glucose metabolism and immune response.
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DHEA
Major adrenal androgen, influences libido in females.
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Adrenal Medulla
Releases adrenaline and noradrenaline during stress.
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Catecholamines
Hormones released by adrenal medulla, enhance fight-or-flight.
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Eustress
Positive stress that prepares for challenges.
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Distress
Negative stress that can be harmful.
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Fight-or-Flight Response
Initial stress response, prepares body for action.
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Resistance Reaction
Longer stress response involving cortisol and glucocorticoids.
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Cortisol
Stress hormone that increases glucose availability.
101
Thyroid Hormone Functions
Regulates metabolism, growth, and development.
102
What is the primary factor determining sexual differentiation in human embryos?
Genotype (usually XX or XY) and hormones.
103
What is the significance of primordial germ cells (PGCs) in sexual development?
PGCs migrate from the yolk sac into the urogenital ridge around week 6, creating ovarian and testicular tissue.
104
What hormone maintains the Paramesonephric duct in XX embryos?
Oestrogen.
105
What hormone stimulates degeneration of the Paramesonephric ducts in XY fetuses?
Anti-Mullerian Hormone (AMH).
106
What does the genital tubercle develop into in females?
The clitoris.
107
What does the genital tubercle develop into in males?
The glans penis.
108
What are the three main activities controlled by the female reproductive cycle?
Ovarian cycle, uterine cycle, and cervical cycle.
109
What initiates the reproductive cycle at puberty?
Gonadotropin releasing Hormone (GnRH) from the hypothalamus.
110
What hormones are released from the anterior pituitary during puberty?
Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH).
111
What is the role of FSH in the female reproductive cycle?
Stimulates growth of follicular cells and production of oestrogen.
112
What is the function of progesterone during the luteal phase?
Thickens cervical mucus and supports the uterine lining for potential implantation.
113
What is the process of meiosis in oocyte formation?
Generates four daughter cells from the original cell, with one becoming the functional ovum and the others degrading as polar bodies.
114
What is the duration of sperm production (spermatogenesis)?
65 to 75 days.
115
What are the stages of spermatogenesis?
A-spermatogonium, B-spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid, sperm cell.
116
What is the role of Leydig cells in the male reproductive system?
Produce testosterone.
117
What is the role of Sertoli cells in the male reproductive system?
Support germ cell development and provide nourishment.
118
What is Early Pregnancy Factor and its role?
An immunosuppressant found in the bloodstream shortly after conception that stimulates trophoblast growth.
119
What hormones increase during early pregnancy?
Progesterone, oestrogen, and human Chorionic Gonadotrophin (hCG).
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What hormones decrease during early pregnancy?
Gonadotropin Releasing Hormone (GnRH), Follicle Stimulating Hormone (FSH), and Luteinising Hormone (LH).
121
What is the role of the placenta during pregnancy?
Takes over hormone production from the corpus luteum and supports fetal growth.
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What is the significance of hormonal feedback in the reproductive system?
Controls hormone levels to maintain reproductive functions and cycles.
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What are the effects of stress on female reproduction?
Stress may influence fertility and is related to up to 50% of cases of female infertility.
124
What happens to hormone levels if pregnancy does not occur?
Falling levels of progesterone, oestrogen, and inhibin lead to menstruation and increased GnRH.
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What is the role of oestrogen in the uterine cycle?
Stimulates growth of the uterine lining to prepare for implantation.
126
What changes occur in cervical mucus during the ovulatory phase?
Mucus becomes more fluid and alkaline to promote sperm survival and facilitate entry.
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What is the importance of the hypothalamo-pituitary-gonadal axis?
Regulates reproductive hormone release and feedback mechanisms.
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Conceptus (Pre-organogenesis)
Cell division, polarization, formation of bilaminar germ disc.
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Embryo
Gastrulation (formation of trilaminar germ disc), basic body plan, organogenesis.
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Fetus
Growth, refinement, and functional maturation.
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Morula
A solid ball of cells (8+), characterized by hyperplasia (cell division without growth).
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Blastomere
Individual cell within the morula.
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Compaction
Formation of a tightly packed morula.
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Blastocyst
Hollow ball of cells with a cavity called blastocoel, contains inner cell mass (ICM) which contributes to embryo formation.
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Blastocoel
Fluid-filled cavity inside the blastocyst.
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Embryonic Stage
Initial organ structures formed.
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Fetal Stage
Basic body plan established; characterized by growth and refinement (e.g., differentiation of hand plates).
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Mammalian Cleavage
Slow and regulated cleavage (~12-24 hours per division in humans).
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Sea Urchin Cleavage (Holoblastic)
Rapid and complete cell divisions with equal-sized blastomeres.
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Amphibian Cleavage
Unequal holoblastic cleavage.
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Avian (Chick) Cleavage (Meroblastic)
Incomplete cleavage; does not fully divide the yolk.
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Epiblast
Outer layer, forms embryonic tissues, surrounds amniotic cavity.
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Hypoblast
Primitive endoderm, forms extraembryonic tissues, faces yolk sac.
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Gastrulation
Formation of three primary germ layers (ectoderm, mesoderm, endoderm).
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Ectoderm
Forms skin and nervous system.
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Mesoderm
Forms internal organs.
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Endoderm
Forms internal linings (gut, blood vessels).
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Gastrulation in Sea Urchins
Cells move towards vegetal pole, undergo shape changes and invagination.
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Gastrulation in Amphibians
Grey crescent cells form dorsal blastopore.
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Gastrulation in Chicks
Primitive streak (Henson's node) forms.
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Gut Formation during Gastrulation in Mammals
Endoderm folds downward, pinches off to form gut.
152
Structure of a sperm cell
Head: Contains nucleus and acrosome. Midpiece: Packed with mitochondria for energy. Tail (flagellum): Provides motility.
153
External fertilisation
Fertilisation occurs outside the body. Seen in species like sea urchins, producing large, transparent embryos.
154
Five steps of sea urchin fertilisation
Contact, Acrosomal reaction, Fusion of sperm and egg membranes, Cortical reaction, Entry of sperm nucleus.
155
Acrosomal reaction in sea urchins
Acrosome releases enzymes to break down the egg's outer layers. Forms the acrosomal process with bindin to interact with the bindin receptor on the egg's vitelline membrane.
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Fast block to polyspermy
Fusion of sperm and egg membranes causes Na⁺ ion influx. Leads to membrane depolarisation. Prevents additional sperm from fusing temporarily.
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Slow block to polyspermy in sea urchins
Ca²⁺ wave from ER activates the cortical reaction. Cortical granules release enzymes to modify the egg membrane. Hardens the fertilisation envelope, preventing further sperm entry.
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Changes in egg activation
Protein synthesis and metabolic activity increase. Male and female pronuclei migrate and fuse, forming a zygote. DNA replication begins for cleavage division.
159
State of the human egg at ovulation
Human oocyte is arrested at metaphase of meiosis II. Surrounded by corona radiata (granulosa cells + hyaluronic acid) and zona pellucida (glycoprotein layer).
160
Sperm penetration of human egg's protective layers
Sperm must undergo capacitation. Hyaluronidase helps sperm penetrate the corona radiata. Acrosomal reaction releases enzymes to digest zona pellucida.
161
Molecular interactions between sperm and egg in mammals
ZP3 glycoprotein binds to β1-4-galactosyltransferase on sperm → triggers acrosomal contents release. Enzymes acrosin and β-N-acetylglucosaminidase digest zona glycoproteins.
162
Essential proteins for mammalian sperm-egg membrane fusion
Izumo1 on sperm binds to Juno on oocyte. Other proteins: CD9, SPACA6 assist membrane fusion. Triggers Ca²⁺ release → exocytosis of vesicles to harden zona pellucida.
163
After sperm entry into the human oocyte
Entire sperm absorbed → oocyte resumes meiosis II. Forms a haploid ovum and second polar body. Female pronucleus develops.
164
Pronucleus formation and preparation for cleavage
Male pronucleus forms; spindle fibres from centrosome prepare first division. DNA replication occurs. Pronuclei fuse to form the zygote.
165
First cleavage division
Chromosomes align on the metaphase plate. Spindle attaches chromosomes → first mitotic division of the zygote begins.
166
Recent discovery using AlphaFold
AI used to model sperm-egg protein interactions. Identified TMEM81 alongside known proteins Izumo1 and SPACA6 as part of sperm protein complex binding Juno on the egg.
167
Pregnancy
40 weeks, 240 days, 10 months.
168
Clinical counting
Starts from Last Menstrual Period (LMP).
169
Preorganogenesis
2-4 weeks LMP.
170
Embryonic period
5-10 weeks LMP: organogenesis.
171
Fetal period
11 weeks LMP onwards: functional and final structure formation.
172
Teratogens
Substances causing malformation (e.g. alcohol, drugs, vitamin A, rubella).
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Greatest risk of teratogen exposure
First trimester → major malformations occur during embryonic period.
174
Spina Bifida
Failure of neural tube closure at spinal ends.
175
Detection of Spina Bifida
Detected by α-fetoprotein levels and ultrasound scans.
176
Rubella Virus Syndrome
Mild in adults, severe in fetus if contracted in early pregnancy.
177
Symptoms of Rubella Virus Syndrome
Cataracts, deafness, congenital heart defects, mental and physical disabilities.
178
MMR vaccination
Prevents maternal infection of Rubella Virus.
179
Human Chorionic Gonadotrophin (hCG)
Detectable by week 4 (8 days post-fertilisation).
180
Role of hCG
Maintains corpus luteum to support pregnancy; failure leads to miscarriage.
181
Physiological changes during pregnancy
Increased heart rate, respiratory rate, blood volume.
182
Ectopic pregnancy
Implantation occurs in fallopian tube instead of uterus.
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Signs of ectopic pregnancy
Unilateral pain, shoulder pain, vaginal bleeding.
184
Gestational trophoblastic tumours
Rare, abnormal overgrowth of trophoblast tissue.
185
Types of gestational trophoblastic tumours
Hydatiform mole (benign), sometimes progressing to choriocarcinoma.
186
Common problems of later pregnancy
Gestational diabetes (4-5%), pre-eclampsia, obstetric cholestasis, gestational thyrotoxicosis.
187
Stages of implantation
Zygote forms → morula → blastocyst.
188
Blastocyst attachment
Attaches to uterine wall ~day 6 post-fertilisation.
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Cytotrophoblast
Dense inner cells forming placental villi.
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Syncytiotrophoblast
Invasive outer cells forming lacunae, secretes hCG, creates barrier between fetal and maternal blood.
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Placental circulation
Maternal blood flows into intervillous lakes.
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Functions of the placenta
Protection, gas exchange, nutrition, waste elimination.
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Hormone production by the placenta
hCG, progesterone, oestrogen, placental prolactin, placental lactogen, relaxin.
194
Haemolytic disease of the fetus
Caused by maternal Rh-negative blood reacting to fetal Rh-positive cells.
195
Consequences of haemolytic disease
Can lead to severe anemia → hydrops fetalis.
196
placental circulation
•Maternal blood flows into intervillous lakes (not lacunae) •chorionic villi (Villous trees) grow into lakes•Blood flows into these capillaries from the embryonic heart, via the umbilical arteries.•Fetal blood picks up oxygen and nutrients from the maternal blood. Returns to fetus•Fetal blood (Hb)has a higher affinity for Oxygen•Fetal blood supply relatively deoxygenated•Maternal and Fetal blood supplies ALWAYS separated by syncitiotrophoblast
197
Fertilisation
≈ day 14 LMP.
198
Preorganogenesis
2-4 weeks LMP.
199
Embryonic period
3-10 weeks LMP (organogenesis).
200
Fetal period
11 weeks+ (functionality and growth).
201
Early pregnancy factor
Detected at 2-3 days post-fertilisation.
202
hCG
Detectable by day 8.
203
Gastrulation
Forms ectoderm, mesoderm, endoderm by week 4.
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Ectoderm
Nervous system, skin.
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Mesoderm
Musculoskeletal, cardiovascular.
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Endoderm
GI tract, lungs.
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Caudal dysgenesis (sirenomelia)
Linked to maternal diabetes.
208
Situs inversus
Reversal of internal organs.
209
Sacrococcygeal teratoma
Tumour from primitive streak.
210
Neurulation
Initiated during weeks 4-6.
211
Heart tube
Starts beating by week 5.
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Neural tube closure
Begins around day 24.
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Anencephaly
Failure of neural tube closure.
214
Spina bifida
Linked to folic acid deficiency.
215
Congenital disorders
Neural tube defects (anencephaly, spina bifida).
216
Fetal transition
Tooth buds and long bone ossification at 8-12 weeks.
217
Omphalocoele
Gut fails to retract (2.5/10,000 births).
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Myelination of neurons
Begins at 12-16 weeks.
219
Surfactant
Starts to be produced at 16-20 weeks.
220
Factors contributing to secondary infertility
Age, health conditions, medication, weight gain, scarring (e.g. from PID), fibroids, infections. Social stigma and psychological stress also play a role.
221
Role of the HFEA and the Human Fertility and Embryology Act 1990
Regulates all UK fertility treatments. Licenses clinics and ensures safe, ethical treatment practices.
222
Intrauterine insemination (IUI)
Sperm is placed high in the uterus. Used for idiopathic infertility, paraplegia, obstructed vas deferens, same-sex couples, or post-mortem. Average success: ~15.8% for women under 35, decreasing with age.
223
Swim-up sperm selection technique
Semen sample is layered under media. Motile, healthy sperm swim up into the top layer and are collected for use.
224
Basic steps of IVF
Hormonal suppression of natural cycle. Stimulation of oocyte growth (FSH, clomiphene). Oocyte retrieval by transvaginal aspiration. Fertilisation with sperm outside the body. Healthy embryo transfer to uterus.
225
ICSI
Intracytoplasmic sperm injection: directly injects a single sperm into an egg. Used when sperm quality is poor (motility, morphology, count) or sperm are frozen.
226
Frozen embryo transfer (FET)
Transfer of previously frozen embryos. Gives time for patient recovery, allows genetic testing, can improve success rate and reduce risks (e.g., maternal bleeding).
227
Embryo quality assessment in IVF
Day 1: Fertilised egg with 2 pronuclei. Day 2: 4 cells. Day 3: 6-8 cells. Day 5: Blastocyst with Inner Cell Mass (ICM) and well-formed trophoblast.
228
Risks and side effects of IVF
Emotional strain, high cost, discomfort. Superovulation can cause multiple births, ectopic pregnancy, or Ovarian Hyperstimulation Syndrome (OHSS).
229
Ovarian Hyperstimulation Syndrome (OHSS)
Increased capillary permeability → oedema, possible renal failure. Occurs in 8% mild cases, <1% severe cases.
230
Sperm quality evaluation for assisted reproduction
Assessed for motility, morphology, concentration. Abnormalities: multiple heads, two tails, poor motility. Sperm retrieval may be needed if azoospermia is present.
231
IVF considerations for transgender individuals
Trans women may require stimulation with clomiphene or hCG to produce sperm. Trans men must pause testosterone therapy (3-6 months) to resume ovulation.
232
Male infertility taboo
Lack of awareness and discussion. Emotional and social stigma for men. Under-addressed in reproductive healthcare discussions.
