Urine Storage Capacity: The bladder can store approximately 3 liters of urine, with around 100 mL present at the time of reflex.
Storage Reflex:
This reflex allows the bladder to store urine without voiding.
The detrusor muscle—composed of smooth muscle layers—relaxes during urine storage.
The internal sphincter is contracted to prevent urine from exiting.
The external sphincter, which is voluntary, remains contracted to maintain urine storage.
Detrusor Muscle and Urination Control
Detrusor Muscle:
Comprises layers of smooth muscle around the bladder, oriented in different directions.
Responsible for bladder contraction during urination.
Sphincters:
Internal Sphincter: Involuntary control.
External Sphincter: Voluntary control, affected by conscious brain decisions through the central nervous system.
Signals and Potty Training
As the bladder fills, pressure receptors signal fullness.
Signals are sent to the cerebral cortex, necessary for voluntary control over micturition.
The pons also plays a role in involuntary responses, which can take precedence if the bladder fills too much, triggering involuntary urination to prevent damage.
Overview of Reproduction and Cell Division
Mitosis:
Defined as a cell division process that replicates cells, leading to two identical cells (genetic clones).
Meiosis:
A specialized form of cell division that reduces the chromosome number by half to produce gametes.
Involves two divisions: Meiosis I and Meiosis II.
Chromosome Number and Gamete Formation
Chromosome Basics:
Humans have 46 chromosomes (23 pairs) in somatic cells.
Gametes (sperm and eggs) each have 23 chromosomes.
This reduction is due to meiosis, maintaining genetic consistency in offspring (46 chromosomes as diploids).
Process of Meiosis
Meiosis I: Separates homologous chromosomes; reduces chromosome number by half (23).
Meiosis II: Similar to mitosis, separates sister chromatids.
Random assortment and crossing over during meiosis generate genetic diversity, crucial for evolution.
Gametogenesis
Spermatogenesis:
Male gamete formation; each spermatocyte produces four sperm cells through meiosis.
Oogenesis:
Female gamete formation; results in one egg and polar bodies (degenerate and reabsorbed).
Oocytes undergo meiosis, phylogenetically conserving cytoplasmic resources for the egg, crucial for embryonic development.
The ovum is larger than sperm due to the need for reserves during early development.
Ovarian Follicle Development
Ovarian follicles evolve through stages—primordial, primary, secondary, to Graafian (mature).
Primordial Follicle: Contains a primary oocyte and squamous follicular cells; present at birth.
Primary Follicle: Follicle cells become cuboidal, starting hormone production.
Secondary Follicle: Fluid-filled spaces form as follicle matures, leading to the Graafian follicle stage.
Graafian Follicle: Expands significantly; prepares for ovulation.
Ovulation: Upon rupture, the oocyte with surrounding cumulus cells is released into the fallopian tube.
Post-Ovulation and Hormonal Function
The remaining cells form the corpus luteum, secreting hormones (progesterone and estrogen) for uterine preparation for potential implantation.
Corpus luteum: Plays a crucial role in the menstrual cycle, degenerating if implantation does not occur, marking the onset of menstruation.