Phys Lab M14

Glomerular Capsule (Bowman's Capsule)

Cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood.

Proximal Convoluted Tubule (PCT)

Tubule section where initial water reabsorption occurs via osmosis as sodium and other solutes are actively reabsorbed into the blood, and where bicarbonate combines with H+ to form carbonic acid.

Juxtaglomerular Cells

Specialized smooth muscle cells in the afferent arteriole that secrete renin in response to low blood pressure or decreased renal perfusion.

Macula Densa

Specialized cells in the distal convoluted tubule that monitor sodium chloride concentration in the filtrate.

Podocytes

Specialized epithelial cells wrapping around glomerular capillaries that form filtration slits to allow passage of small solutes while blocking proteins.

Cortical Nephrons

Nephrons comprising 85% of all renal nephrons, located mostly in the cortex with loops of Henle that dip shallowly into the medulla.

Juxtamedullary Nephrons

Nephrons comprising 15% of renal nephrons, possessing long loops of Henle that extend deep into the renal medulla to concentrate urine.

Kidney pH Regulation via Bicarbonate

In the PCT, filtered HCO3- combines with H+ to form H2CO3, which breaks into CO2 and H2O; inside cells, carbonic anhydrase converts CO2 back to H2CO3, dissociating into HCO3- (reabsorbed into blood) and H+.

Kidney pH Regulation via Hydrogen Secretion

In response to acidosis, DCT and collecting duct cells actively secrete excess H+ into tubular fluid while generating new HCO3- for the blood to maintain a blood pH near 7.4.

ADH (Antidiuretic Hormone) Mechanism

Released from the posterior pituitary in response to high solute concentration or low blood volume; stimulates aquaporin channel insertion in collecting ducts to increase water reabsorption.

Excretion in Fluid Balance

When blood volume is adequate and osmolarity is low, ADH levels drop, making collecting ducts less permeable to water so excess water is excreted in urine.

Aldosterone Electrolyte Regulation

Promotes sodium reabsorption in the DCT and collecting ducts by increasing sodium channels and Na+/K+ pumps, while secreting excess potassium into tubular fluid.

PTH (Parathyroid Hormone) Function on Kidneys

Increases calcium reabsorption in distal tubules while decreasing phosphate reabsorption in the PCT (causing excess phosphate excretion).

RAAS Activation Sequence

Low blood pressure -> Renin (from kidneys) converts Angiotensinogen (from liver) to Angiotensin I -> ACE (from lungs) converts Angiotensin I to Angiotensin II.

Angiotensin II Actions

Potent vasoconstrictor that raises blood pressure, stimulates aldosterone release for Na+/water retention, and promotes ADH secretion to increase blood volume.

Oogonia to Primary Oocytes

Before birth, fetal oogonia undergo mitotic division to form millions of primary oocytes that begin meiosis I and arrest in prophase I until puberty.

Primary Oocyte Division at Puberty

LH surges during the ovarian cycle trigger arrested primary oocytes to complete meiosis I, yielding one large secondary oocyte and one small, degenerating first polar body.

Meiosis II in Oogenesis

Secondary oocytes arrest at metaphase II and are ovulated into the fallopian tube; meiosis II only completes upon sperm penetration, producing a mature ovum and a second polar body.

Fate of Unfertilized Secondary Oocyte

If fertilization does not occur within 24 hours, the secondary oocyte degenerates and is shed with the uterine lining during menstruation.

Type A vs. Type B Spermatogonia

Type A spermatogonia remain as stem cells at the outer edge of seminiferous tubules; Type B spermatogonia differentiate into primary spermatocytes (46 chromosomes).

Meiotic Division in Spermatogenesis

Primary spermatocytes (diploid) undergo meiosis I to form 2 secondary spermatocytes (haploid, 23 chromosomes), which undergo meiosis II to form 4 haploid spermatids.

Spermiogenesis Events

Spermatids transform into mature spermatozoa by developing a motility flagellum, condensing genetic material in the head, forming an enzymatic acrosome cap, and shedding excess cytoplasm.

Sperm Maturation Site

Newly formed spermatozoa are transported to the epididymis, where they mature over several days and gain the ability to swim.

Spermatogenesis vs. Oogenesis Timeline

Spermatogenesis begins at puberty, runs continuously throughout life, and takes 64-72 days; oogenesis begins before birth, pauses for decades, and ceases at menopause.

Homologous Chromosomes & Alleles

Humans possess 23 pairs of chromosomes (46 total); genes on these chromosomes exist in variant forms called alleles, receiving one version from each parental gamete.

Homozygous vs. Heterozygous

Homozygous indicates an individual inherited two identical alleles for a gene (e.g., AA or aa); heterozygous indicates two different alleles were inherited (e.g., Aa).

Dominant vs. Recessive Allele Expression

Dominant alleles express their trait with only one copy present (AA or Aa); recessive alleles require two copies (aa) to express the trait.

Genetic Carrier

A heterozygous individual (Aa) carrying one copy of a recessive allele; they do not express the recessive trait themselves but can pass it to offspring.

Punnett Square Purpose

A grid tool mapping parent allele combinations (top and side labels) to calculate the probability of offspring inheriting specific genotypes and phenotypes.