CASE 4 Flashcards
where are sperm made and where do they mature?
made in seminiferous tubules between sertoli cells
mature in epididymis
where is testosterone made?
made in Leydig cells/interstitial cells of Leydig — adjacent to seminiferous tubules
describe the stages of spermatogenesis
- spermatogonium undergoes mitosis
- one of the daughter cells differentiates into a primary spermatocyte
- the primary spermatocyte moves through the tight junction and starts to enlarge (under the influence of testosterone) by increasing its cytoplasm
- tight junction closes quickly
- primary spermatocyte divides into 2 secondary spermatocytes by meiotic division
- secondary spermatocytes differentiate into spermatids (meiosis 2) — 4 spermatids made
- spermiogenesis: spermatids differentiate into spermatozoa (1 spermatozoa per spermatid)
- spermatozoa travel to the epididymis to fully mature — gain mitochondria and longer flagelli
brief summary of spermatogenesis (order)
spermatogonium — mitosis — one differentiates into primary spermatocyte — through tight junction and gets bigger — divides into 2 secondary spermatocytes (meiosis) — differentiate into 4 spermatids (meiosis 2) — turn into spermatozoa
how many sperm does one primary spermatocyte give rise to?
4 sperm
what is a blood testis barrier and what is its function? function of tight junction
= a physical barrier between the blood vessels and the seminiferous tubules of the testes
- produced by tight junctions between sertoli cells
- regulates composition of luminal fluid in which germ cells develop
- prevents sperm antigens from constant with systemic/lymphatic systems causing an immune response to sperm
tight junction closes very quickly — maintains the different environments as not much leakage between compartments
function of testosterone in stimulating spermatogenesis + where is it made?
secreted by the Leydig cells. it is essential for growth and division of the testicular germinal cells = 1st stage of forming sperm
function of LH in stimulating spermatogenesis + where is it made?
secreted by the anterior pituitary gland. stimulates the Leydig cells to secrete testosterone
function of FSH in stimulating spermatogenesis + where is it made?
secreted by the anterior pituitary glad. stimulates the sertoli cells — enables the process of spermiogenesis
function of estrogens in stimulating spermatogenesis + where are they made?
formed from testosterone by the sertoli cells when they are stimulated by FSH
function of growth hormone in stimulating spermatogenesis + where is it made?
(as well as most other body hormones) it is essential for controlling background metabolic functions of the testes. it specifically promotes the early division of the spermatogonia themselves. without it = infertility as spermatogenesis is severely deficient or absent
drugs that modify the action of steroid hormone receptors are based on cholesterol because steroid hormones function by ____ ?
activating intracellular receptors
how do steroid hormones work?
- pass through cell membrane of target cell - possible as they are lipid-soluble so can diffuse through phospholipid bilayer
- binds with receptor in cytoplasm, forming a receptor-hormone complex
- complex enters nucleus and triggers gene transcription
- transcribed mRNA is translated into proteins
how do peptide hormones work?
- a water-soluble peptide hormone (1st messenger) binds to receptor
- this activates a G protein
- G protein activates adenylate cyclase
- adenylate cyclase converts ATP to cAMP
- cAMP acts as a 2nd messenger to activate protein kinases
- protein kinases are enzymes that phosphorylate other proteins
- phosphorylation is carried out by donating a phosphate group : ATP —> ADP
- these phosphorylated proteins cause reactions
- phosphodiesterase inactivates cAMP eventually
- this turns off the cell’s response unless new hormones continue to bind to their receptors in the plasma membrane
where do sperm become motile?
epididymis
if non-disjunction occurred in meiosis 2 of spermatogenesis, at which stage of gamete development would abnormalities in chromosome complement be first apparent?
spermatids
what is the role of the acrosome contents?
acrosome contents usually digest the zona pellucida surrounding the ovum
function and types of bone
long, short, irregular, flat
support, protection, movement, mineral homeostasis, triglyceride storage, blood cell production
where does bone growth occur?
epiphyseal plate
where is the epiphyseal plate and what is it?
metaphysis — joins epiphysis to bone shaft
it is a region of transition from cartilage to bone. consist of typical hyaline cartilage in the middle, with a transitional zone on each side where cartilage is being replaced by bone
what does spongy bone consist of?
full of holes for blood vessels and nerves
where is bone marrow?
in the medullary cavity (hollow)
what is the medullary cavity lined with?
lined with thin membrane that lines the endosteum
what is the periosteum?
tough sheet of dense connective tissue that surrounds bone surface — serves as an attachment point for tendons and ligaments
compact vs spongy (aka. trabecular, cancellous) bone
spongy — adipose tissue with trabecullae
compact — central canal, lamellae, lacuna with osteocytes, canaliculi, Haversian system (osteon)
what travels through the central canal in compact bone?
blood vessels and nerves
what do canaliculi in compact bone allow?
canaliculi in Haversian system allows osteocytes to communicate with each other (canaliculi connect lacunae, osteocytes sit within a lacuna)
what is bone? what does the bone matrix contain?
a highly vascular mineralised connective tissue
matrix — primarily composed of collagen fibres and calcium phosphate
name 4 bone cells and describe them
- osteoprogenitor cell = bone’s stem cells. can differentiate into fibroblasts, osteoblasts, chondrocytes, adipocytes
- osteoblast = secrete collagen and extra cellular matrix. become trapped in matrix
- osteocyte = responsible for maintaining bone matrix and homeostasis. sit within lacuna
- osteoclast = formed by fusion of 50+ monocytes. “bone-chellers” — responsible for removal of bone and break bone down
what does an osteoblast become when it gets trapped in matrix?
osteocyte
what is cartilage and what is the most common type?
an a vascular connective tissue consisting of cells (chondrocytes which sit in lacuna) and matrix (water, collagens, proteoglycons)
what are the 2 different ways bones grow?
OSSIFICATION
- flat bones = intramembranous
- long bones = endochondral
name the 5 different zones in the epiphyseal plate and what hormones work there
- reserve zone - GH
- proliferative zone - GH and IGF-1
- zone of maturation
- zone of degeneration
- zone of provisional calcification
zones 3,4,5 are hypertrophic zones, thyroid hormones act here
describe the zone of reserve cartilage
consists of hyaline cartilage. nothing really happens here
describe the zone of cell proliferation
- chondrocytes proliferate
- chondrocytes, surrounded by lacuna, arrange themselves into longitudinal columns of flattened lacunae
describe the zone of maturation
- chondrocytes stop proliferating
- chondrocytes begin hypertrophy
- chondrocytes secrete collagen type 10, that allows the plates of cartilage to begin calcifying
- this pushes lacunae in the columns further apart
describe the zone of degeneration
- chondrocytes become hypoxic and begin to die
- their contents are secreted into the matrix, causing erosion of the plates of cartilage between the lacunae
- this converts each column into the longitudinal channel
describe the zone of provisional calcification/invasion/angiogenesis
- blood vessels invade these channels
- osteoblasts and progenitor cells line up along the walls of these channels and begin depositing layer after layer of bone matrix
- osteoclasts cause bone resorption
what deposits bone and what resorbs bone?
bone is continuously being deposited by osteoblasts and resorted by osteoclasts
benefits of constant bone deposition and resorption
- bones thicken (in response to heavy loads)
- shape adjusts to stresses placed on bone
- renews matrix — maintains toughness, rate higher in children than adults — old bones are brittle and weal
parathyroid hormone and calcitonin functions
= keep bone calcium levels constant
- low Ca levels — parathyroid released - increases osteoclast activity — resorbs bone to increase calcium ions levels in blood
- high Ca levels — calcitonin released - decreases osteoclast activity
what does the cell cycle consist of?
interphase + M phase
interphase: G1 = cell grows in size and decreases its mass of proteins and organelles. monitors environments
S phase = DNA replication. G2 =another phase of growth and checking
M phase: mitosis + cytokinesis
how do exercise, sleep and gherlin affect growth?
exercise — increase release of GHRH
sleep — increases and decreases release of GHRH
ghrelin — peptide hormone secreted by fundus of the stomach which increases the release of GH
what is GHRH and where is it released?
growth hormone releasing hormone
stimulates synthesis of GH by increasing GH gene transcription and GH release by the somatrophs in the anterior pituitary gland
released by hypothalamus
on what chromosome is the gene for GH located?
chromosome 17