Human Biology: Comprehensive Review of Cellular Processes, Organ Systems, Genetics, and Human Development

Vocabulary practice flashcards covering cell organelles, cellular respiration, transport, body systems, genetics, reproduction, and human embryology from the lecture notes.

Aerobic Respiration

An efficient cellular process that utilizes oxygen to fully break down glucose into carbon dioxide, water, and approximately $36\text{--}38\text{ ATP}$ molecules per glucose molecule, occurring across the cytosol and mitochondria.

Glycolysis

The initial stage of cellular respiration occurring in the cytosol, where glucose is split into two molecules of pyruvate, producing a net yield of $2\text{ ATP}$.

Anaerobic Respiration

The breakdown of glucose in the absence of oxygen occurring solely in the cytosol, converting pyruvate into lactic acid in humans and yielding only $2\text{ ATP}$ molecules per glucose molecule.

Mitochondria

Oval-shaped organelles enclosed by a double membrane with inner folds called cristae; they serve as the primary site of aerobic cellular respiration (Krebs cycle and electron transport chain) to produce ATP.

Ribosomes

Small, spherical structures composed of rRNA and protein that serve as the sites of protein synthesis by linking amino acids together via peptide bonds.

Rough Endoplasmic Reticulum (RER)

A network of flattened membrane sacs studded with ribosomes extending from the nuclear membrane into the cytoplasm; it synthesizes, folds, modifies, and transports proteins to the Golgi apparatus.

Smooth Endoplasmic Reticulum (SER)

A network of membranous tubules lacking ribosomes that synthesizes lipids and phospholipids, produces steroid hormones, detoxifies drugs and harmful substances, and stores calcium ions.

Golgi Apparatus

A series of flattened membrane sacs called cisternae that modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum into vesicles for secretion or delivery to lysosomes.

Lysosomes

Membrane-bound digestive vesicles containing enzymes that break down waste materials, cellular debris, foreign pathogens, and damaged organelles.

Osmosis

The passive diffusion of water molecules across a selectively permeable membrane from an area of high water concentration to an area of low water concentration through aquaporin channels.

Active Transport

The movement of substances across a cell membrane against their concentration gradient (from low to high concentration) utilizing membrane protein pumps and cellular energy in the form of ATP.

Phagocytosis

A form of endocytosis known as 'cell eating,' in which a cell expends energy to engulf large, solid particles or microorganisms into an internal vesicle.

Epiglottis

A flap of elastic cartilage located at the entrance of the larynx that covers the oesophagus during inhalation to direct air into the trachea and covers the larynx during swallowing to prevent food from entering the airway.

Alveoli

Microscopic, one-cell-thick air sacs surrounded by capillary networks that act as the functional units of the lungs, providing a large, moist surface area for gas exchange between air and blood.

Pleura

A double-layered serous membrane that covers the exterior of the lungs and lines the inside of the chest cavity, containing a thin film of pleural fluid between its layers to reduce friction and hold the lungs against the chest wall.

Ventilation

The mechanical process of moving air into and out of the lungs through pressure changes created by the contraction and relaxation of the diaphragm and external intercostal muscles.

Erythrocytes

Biconcave, anucleated blood cells that make up $40\text{--}45\%$ of blood volume (haematocrit), containing haemoglobin to transport oxygen from the lungs to body tissues with an average lifespan of about $120\text{ days}$.

Leucocytes

White blood cells making up approximately $1\%$ of total blood volume that protect the body against infectious diseases and foreign invaders, including neutrophils, monocytes, lymphocytes, basophils, and eosinophils.

Thrombocytes

Small cell fragments (platelets) that adhere to damaged vascular walls and release substances that stimulate vasoconstriction and provide a scaffold for blood clot formation.

Coagulation

The biochemical formation of a blood clot wherein insoluble protein threads of fibrin form a mesh that traps erythrocytes, platelets, and plasma at a site of injury.

Pericardium

The fibrous membrane completely enclosing the heart within the mediastinum, protecting it and preventing it from overstretching.

Systole

The active pumping phase of the cardiac cycle during which the heart muscle contracts to force blood out of the heart chambers and into the arteries.

Diastole

The filling phase of the cardiac cycle during which the heart muscle relaxes, allowing the atria and ventricles to fill with blood.

Cardiac Output

The volume of blood pumped from a single ventricle of the heart each minute, calculated using the equation $\text{Cardiac output (mL/min)} = \text{stroke volume (mL)} \times \text{heart rate (bpm)}$.

Peristalsis

Waves of circular and longitudinal smooth muscle contractions that narrow the alimentary canal and propel food through the digestive tract.

Chyme

The thick, soupy, semi-fluid mixture of partially digested food and acidic gastric secretions produced by the churning action of the stomach.

Pepsin

The active proteolytic gastric enzyme converted from pepsinogen in the presence of hydrochloric acid at $\text{pH } 2\text{--}3$, responsible for breaking down proteins into shorter peptide chains.

Pyloric Sphincter

A circular muscular band at the lower junction of the stomach that regulates the gradual release of chyme into the duodenum.

Villi

Tiny, finger-like mucosal projections lining the wall of the small intestine that increase the surface area available for the absorption of digested nutrients.

Lacteal

A central lymphatic capillary located within an intestinal villus that absorbs recombined dietary fats, fatty acids, glycerol, and fat-soluble vitamins.

Coeliac Disease

An inherited autoimmune condition in which ingestion of the protein gluten causes immune destruction of the intestinal villi, resulting in malabsorption and malnutrition.

Deamination

An enzymatic process occurring in the liver wherein the amino group ($\text{NH}_2$) is removed from excess amino acids, converting it into toxic ammonia and subsequently into urea for excretion.

Nephron

The microscopic structural and functional unit of the kidney, consisting of a renal corpuscle and a renal tubule, responsible for filtering blood and producing urine.

Glomerular Filtration

The non-selective process in the renal corpuscle where high blood pressure forces water and small dissolved solutes out of the glomerulus across two cellular layers into the glomerular capsule, generating filtrate.

Facultative Reabsorption

The hormonally regulated active reabsorption of water across the renal tubule membranes according to the body's hydration requirements.

Tubular Secretion

The transport of substances such as hydrogen ions, potassium ions, creatinine, and penicillin from the peritubular capillaries into the renal filtrate to regulate blood and urine pH and eliminate wastes.

Haemodialysis

An artificial kidney procedure that removes waste products and excess water from a patient's blood by passing it through fine semi-permeable tubes surrounded by a dialysing fluid bath.

Peritoneal Dialysis

A dialysis method that uses the patient's own highly vascular peritoneum as a semipermeable membrane across which waste products diffuse from blood into dialysing fluid infused into the abdominal cavity via a catheter.

Sarcomere

The contractile repeating structural unit of a myofibril bounded by successive Z lines, comprising overlapping arrays of thick myosin and thin actin filaments.

Sliding Filament Theory

The scientific model explaining muscle contraction, where thin actin filaments slide inward over thick myosin filaments in response to nerve stimulation and ATP hydrolysis, pulling Z lines closer and shortening the sarcomere.

Antagonist Muscles

Pairs of skeletal muscles that produce opposing movements at a joint, where contraction of the agonist (prime mover) is matched by relaxation of the antagonist.

Osteon

The basic structural unit of compact bone (Haversian system), consisting of concentric layers of bony matrix called lamellae arranged around a central Haversian canal containing blood vessels and nerves.

Hyaline Cartilage

A connective tissue containing closely packed, ultra-fine collagenous fibres within a chondrin matrix that provides strength and flexibility, found in the articular ends of bones, tracheal rings, and bronchi.

Synovial Joint

A freely movable joint characterized by a fluid-filled synovial cavity, an outer fibrous capsule, an inner synovial membrane, and articulating surfaces capped with articular cartilage.

Osteoporosis

A progressive bone disease characterized by significant loss of bone mass and mineral density, which leaves bones brittle, porous, and highly susceptible to fractures.

Osteoarthritis

A degenerative joint disease typically associated with aging where articular cartilage wears away, exposing underlying bone surfaces to friction and triggering the formation of bony spurs.

Nucleotide

The repeating monomer unit of nucleic acids, consisting of a five-carbon sugar molecule (deoxyribose in DNA or ribose in RNA), a phosphate group, and a nitrogenous base.

Histones

A group of eight specialized proteins around which long DNA strands wrap to form nucleosomes, facilitating the efficient packaging of chromatin within the cell nucleus.

Mitochondrial DNA (mtDNA)

Small, circular, double-stranded DNA molecules found inside mitochondria that are not bound to histones and contain $37\text{ genes}$ essential for mitochondrial respiration and tRNA synthesis.

Transcription

The synthesis of an mRNA molecule from a DNA template strand inside the nucleus, catalyzed by the enzyme RNA polymerase.

Translation

The assembly of a specific sequence of amino acids into a polypeptide chain at a ribosome in the cytosol, guided by the sequence of codons on an mRNA transcript.

Codon

A specific sequence of three consecutive nitrogenous bases on an mRNA strand that codes for a single amino acid or signals the start or termination of protein translation.

Epigenetics

The study of heritable alterations in gene expression that do not involve changes to the underlying nucleotide sequence of the DNA molecule.

DNA Methylation

The chemical addition of methyl groups ($\text{CH}_3$) to DNA molecules, commonly at cytosine-guanine (CpG) dinucleotide sites, which restricts RNA polymerase access and inhibits gene transcription.

Cell Cycle

The repeating sequence of events from one cell division to the next, consisting of interphase (G1, S, and G2 phases) followed by nuclear division (mitosis) and cytokinesis.

Mitosis

The nuclear division of a somatic parent cell into two genetically identical daughter nuclei, each possessing the full diploid number of chromosomes ($2n = 46$ in humans).

Totipotent Stem Cells

Undifferentiated cells present during the first few divisions after fertilisation that possess the developmental potential to produce any body cell type as well as extraembryonic tissues such as the placenta.

Pluripotent Stem Cells

Stem cells derived from the inner cell mass of a blastocyst that can give rise to all specialized cells of the human body, but cannot form extraembryonic tissues.

Multipotent Stem Cells

Partially differentiated stem cells capable of giving rise only to a limited range of specialized, functionally related cell types, such as blood stem cells producing blood components.

Meiosis

A two-stage reductional cell division ($\text{Meiosis I}$ and $\text{Meiosis II}$) occurring in gonads that replicates DNA once to produce four genetically distinct haploid ($n = 23$) gametes.

Homologous Chromosomes

Pairs of matching maternal and paternal chromosomes that are identical in size and shape and carry genes controlling the same inherited characteristics at matching loci.

Crossing Over

The reciprocal exchange of genetic segments between non-sister chromatids of paired homologous chromosomes at chiasmata during prophase I of meiosis, creating new allele combinations.

Non-disjunction

The failure of paired homologous chromosomes or sister chromatids to separate properly during meiotic division, resulting in daughter cells with abnormal chromosome counts ($22$ or $24$ chromosomes).

Metastasis

The dissemination and colonization of malignant tumour cells from an initial primary site through blood or lymph vessels into secondary locations in the body.

Spermatogenesis

The continuous process occurring within the seminiferous tubules of the testes over approximately $72\text{ days}$, whereby diploid spermatogonia divide and differentiate into mature haploid spermatozoa.

Acrosome

A specialized fluid-filled cap at the head of a spermatozoon containing digestive enzymes that break down the protective corona radiata and zona pellucida of an oocyte during fertilisation.

Oogenesis

The cyclical production of female gametes in the ovaries, beginning before birth and resuming at puberty, which ultimately yields a single functional ovum and non-viable polar bodies from each primary oocyte.

Follicle-Stimulating Hormone (FSH)

An anterior pituitary gonadotropic hormone that stimulates the growth and development of ovarian follicles in females and stimulates sperm production in the seminiferous tubules in males.

Luteinising Hormone (LH)

A gonadotropic hormone secreted by the anterior pituitary that stimulates testosterone secretion by interstitial cells in males, and promotes final follicle maturation, ovulation, and corpus luteum formation in females.

Ovarian Cycle

The repeating sequence of events occurring in the ovaries over an average span of $28\text{ days}$, involving the maturation of an ovarian follicle, ovulation of an oocyte, and formation and degeneration of the corpus luteum.

Corpus Luteum

A temporary endocrine structure formed from the collapsed follicle cells after ovulation that secretes progesterone and oestrogen to prepare and maintain the endometrium for potential implantation.

Menarche

A female's first menstrual period, signaling the onset of puberty and the start of reproductive cyclicity.

Corona Radiata

An outer protective layer of follicular cells cemented together by acid surrounding a freshly ovulated secondary oocyte.

Zona Pellucida

A thick, acellular glycoprotein matrix immediately surrounding the plasma membrane of a secondary oocyte that triggers the sperm's acrosome reaction upon binding.

Blastocyst

An early embryonic stage reached approximately six days after fertilisation, consisting of a hollow, fluid-filled sphere of cells containing an inner cell mass that will develop into the embryo.

Ectoderm

The outermost primary germ layer that gives rise to the epidermis of the skin, hair, nails, tooth enamel, the entire nervous system, and the adrenal medulla.

Mesoderm

The middle primary germ layer that differentiates into skeletal, smooth, and cardiac muscles, bone, cartilage, connective tissues, the circulatory system, kidneys, and gonads.

Endoderm

The innermost primary germ layer that forms the epithelial lining of the alimentary canal and associated glands (liver and pancreas), the respiratory tract, urinary bladder, and thyroid.

Amnion

The innermost extraembryonic membrane that encloses the amniotic cavity and secretes amniotic fluid to cushion the developing embryo against shocks, maintain constant temperature, and allow free movement.

Placenta

A temporary organ formed from maternal uterine tissue and foetal chorion that facilitates nutrient, gas, and waste exchange between maternal and foetal blood and secretes hormones required to sustain pregnancy.

Five-Week Embryo

A human developmental stage marked by rapidly elongating arm and leg buds, following the initial appearance of throat clefts and mesodermal blocks in week four.

Foetal Circulation Shunts

Temporary vascular structures present before birth—comprising the ductus venosus, ductus arteriosus, and foramen ovale—that divert oxygen-rich placental blood away from non-functional foetal lungs and liver.

Teratogen

An environmental agent or chemical—such as thalidomide, alcohol, or rubella virus—capable of causing congenital physical defects or developmental abnormalities in an embryo or foetus.