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Semester 1: Physiology and Cell Biology
Cell junctions, cell adhesion molecules, tissues and cell cycle
Cell junctions, cell adhesion molecules, tissues and cell cycle
Cell Junctions
Cell junctions are specialized structures that connect cells to one another, facilitating communication and structural integrity within tissues. They are critical for the organization of tissues and the maintenance of function. Major types of cell junctions include tight junctions, adhering junctions (desmosomes), and gap junctions. Tight junctions prevent the passage of substances between cells, desmosomes provide mechanical strength, and gap junctions allow for the transfer of ions and small molecules.
Cell Adhesion Molecules (CAMs)
Cell adhesion molecules are proteins located on the cell surface that facilitate cell-cell and cell-extracellular matrix adhesion. These include cadherins, integrins, selectins, and immunoglobulin superfamily CAMs. CAMs play a vital role in maintaining tissue architecture, mediating cellular signaling, and influencing cell behavior in processes such as development, immune response, and wound healing.
Tissues
Tissues are groups of cells that work together to perform specific functions. They are classified into four basic types: epithelial, connective, muscle, and nervous tissues. Epithelial tissue covers body surfaces and lines cavities, connective tissue supports and binds other tissues, muscle tissue is responsible for movement, and nervous tissue is involved in communication and control. The organization and interaction between cells within tissues are largely facilitated by cell junctions and CAMs.
Cell Cycle
The cell cycle is the series of phases that a cell goes through as it grows and divides. It consists of interphase (G1, S, G2) and the mitotic phase (M). During interphase, the cell grows, replicates its DNA, and prepares for mitosis. The regulation of the cell cycle is crucial for cell reproduction and overall organism health. Dysregulation can lead to diseases such as cancer. The interplay between cell junctions and the cell cycle is vital for coordinating cell proliferation and maintaining tissue integrity.
Reproductive system: sexual differentiation, sperm transport, menstrual cycle, fertilization
Reproductive system: sexual differentiation, sperm transport, menstrual cycle, fertilization
Sexual Differentiation
Sexual differentiation is the process by which individuals develop male or female phenotypes based on genetic and environmental factors. This process begins at conception with the determination of sex chromosomes, where XY corresponds to male and XX corresponds to female. The Y chromosome carries the SRY gene, which triggers the formation of testes and the production of male hormones, leading to male characteristics. In the absence of SRY, ovaries develop, and female characteristics are promoted by hormones such as estrogen.
Sperm Transport
Sperm transport involves the journey of sperm from the male reproductive tract to the female reproductive tract. After spermatogenesis in the testes, sperm are stored in the epididymis. During ejaculation, sperm travel through the vas deferens, mix with seminal fluid from the seminal vesicles and prostate, and are expelled through the urethra. Sperm then enter the female reproductive tract, where they must navigate through the cervix and uterus to reach the fallopian tubes for potential fertilization.
Menstrual Cycle
The menstrual cycle is a monthly cycle that prepares the female body for pregnancy. It is divided into several phases: the follicular phase, ovulation, the luteal phase, and menstruation. The cycle is regulated by hormones such as FSH, LH, estrogen, and progesterone. The follicular phase involves the maturation of ovarian follicles, ovulation is the release of an egg from the ovary, the luteal phase prepares the uterus for implantation, and if fertilization does not occur, menstruation begins, shedding the uterine lining.
Fertilization
Fertilization is the process by which a sperm cell merges with an ovum to form a zygote. This usually occurs in the fallopian tubes. Sperm must undergo capacitation, allowing them to penetrate the zona pellucida, which surrounds the ovum. Upon successful penetration, the sperm's genetic material combines with the ovum, resulting in the formation of a zygote. This zygote then undergoes cleavage as it travels to the uterus for implantation.
Digestive system: structure, digestion and absorption, bile salts, enzymes, hormones
Digestive system: structure, digestion and absorption, bile salts, enzymes, hormones
The digestive system consists of the alimentary canal and accessory organs. The alimentary canal includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. Accessory organs include the salivary glands, liver, gallbladder, and pancreas.
Digestion involves the mechanical and chemical breakdown of food into smaller components that can be absorbed by the body. The primary sites of digestion are the stomach and small intestine. Absorption primarily occurs in the small intestine, where nutrients pass through the intestinal walls into the bloodstream.
Bile salts are derived from cholesterol and are produced by the liver. They play a crucial role in the emulsification of fats, breaking down large fat globules into smaller droplets, which increases the surface area for digestive enzymes.
Digestive enzymes facilitate the breakdown of macromolecules. Key enzymes include amylase (breaks down carbohydrates), pepsin (breaks down proteins), and lipase (breaks down fats). Enzymes are secreted by various organs including the salivary glands, stomach, and pancreas.
Various hormones regulate digestion. For example, gastrin stimulates gastric acid secretion, secretin regulates bicarbonate secretion from the pancreas, and cholecystokinin (CCK) stimulates bile release from the gallbladder and enzyme secretion from the pancreas.
Respiratory system: gas transport, oxygen and carbon dioxide binding
Respiratory system: gas transport, oxygen and carbon dioxide binding
Overview of the Respiratory System
The respiratory system includes structures involved in the exchange of gases. It consists of the airways, lungs, and circulatory systems that work together to ensure oxygen supply and carbon dioxide removal from the body.
Gas Exchange Mechanism
Gas exchange occurs in the alveoli, tiny air sacs in the lungs. Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli to be exhaled.
Oxygen Transport
Oxygen is primarily transported in the blood bound to hemoglobin, a protein within red blood cells. Each hemoglobin molecule can bind up to four oxygen molecules, maximizing oxygen transport efficiency.
Carbon Dioxide Transport
Carbon dioxide is transported in three forms: dissolved in plasma, bound to hemoglobin, and as bicarbonate ions (HCO3-) formed in red blood cells. Most CO2 is converted to bicarbonate for efficient transport.
Factors Affecting Gas Binding
The affinity of hemoglobin for oxygen is influenced by factors like pH, temperature, and levels of carbon dioxide. The Bohr effect describes how increased CO2 or decreased pH lowers hemoglobin's affinity for O2, facilitating oxygen release in tissues.
Clinical Significance
Understanding gas transport and binding is crucial for managing respiratory diseases. Conditions like anemia, chronic obstructive pulmonary disease, and pneumonia can impair gas exchange and transport, leading to tissue hypoxia.
Nervous system: nerve impulse transmission, neurotransmitters, retina and muscle contraction
Nervous system: nerve impulse transmission, neurotransmitters, retina and muscle contraction
Nerve Impulse Transmission
Nerve impulses are electrical signals that propagate along the axon of a neuron. They are initiated when a stimulus causes the depolarization of the neuron's membrane. This triggers the opening of voltage-gated sodium channels, allowing sodium ions to flow into the cell, creating action potential. The impulse travels down the axon through a process called saltatory conduction, where the impulse jumps between nodes of Ranvier, increasing transmission speed.
Neurotransmitters
Neurotransmitters are chemical messengers that transmit signals across a synapse from one neuron to another. Common neurotransmitters include acetylcholine, serotonin, dopamine, and norepinephrine. When an action potential reaches the axon terminal, neurotransmitters are released into the synaptic cleft, binding to receptors on the postsynaptic neuron, leading to various physiological responses.
Retina Structure and Function
The retina is a layer of tissue at the back of the eye containing photoreceptor cells known as rods and cones. Rods are responsible for vision in low light, while cones provide color vision and detail in bright light. When light hits these photoreceptors, it is converted into electrical signals that are sent through the optic nerve to the brain for processing.
Muscle Contraction Mechanism
Muscle contraction is initiated by the release of acetylcholine at the neuromuscular junction. This leads to depolarization of the muscle fiber and calcium release from the sarcoplasmic reticulum. Calcium binds to troponin, causing a conformational change that moves tropomyosin away from actin binding sites, allowing myosin heads to attach to actin and pull, resulting in muscle contraction. The process of contraction and relaxation is regulated by ATP availability.
Hormones: classification, biosynthesis, mechanism of action, major endocrine glands
Hormones: classification, biosynthesis, mechanism of action, major endocrine glands
Classification of Hormones
Hormones can be classified based on their origin, structure, and function. The main categories include: 1. Steroid Hormones - derived from cholesterol, include sex hormones and corticosteroids. 2. Peptide Hormones - composed of amino acids, include insulin and glucagon. 3. Amino Acid Derivatives - derived from single amino acids, include thyroid hormones and catecholamines.
Biosynthesis of Hormones
The biosynthesis of hormones varies depending on their classification: 1. Steroid Hormones - synthesized from cholesterol in the adrenal cortex, gonads, and placenta. Conversion pathways involve specific enzymes. 2. Peptide Hormones - synthesized in ribosomes of endocrine cells, processed in the endoplasmic reticulum and Golgi apparatus, stored in vesicles until secretion. 3. Amino Acid Derivatives - synthesized from precursor amino acids in specific tissues, such as thyroglobulin for thyroid hormones.
Mechanism of Action of Hormones
Hormones exert their effects through specific mechanisms: 1. Lipophilic Hormones (like steroids) - pass through cell membranes, bind to intracellular receptors, and regulate gene transcription. 2. Hydrophilic Hormones (like peptides) - bind to cell surface receptors, activate signal transduction pathways (e.g., cAMP, calcium-mediated pathways) to elicit a cellular response.
Major Endocrine Glands
1. Pituitary Gland - often termed the 'master gland', regulates other endocrine glands. 2. Thyroid Gland - regulates metabolism and growth through thyroid hormones. 3. Adrenal Glands - produce steroid hormones (cortisol, aldosterone) and catecholamines. 4. Pancreas - regulates blood glucose levels through insulin and glucagon. 5. Gonads (Ovaries and Testes) - produce sex hormones that regulate reproductive functions.
