Quiz 9 - Spinal reflexes and reproductive systems Flashcards
4 functions of spinal reflexes
- Maintain walking movements
- Withdraw portions of the body from noxious stimuli
- Maintain tone in legs to maintain posture
- Regulate local blood vessels, GI movement, urinary excretion
Reflex Arc
“Local circuit”
Receptor –> Sensory Neuron –> Integration center –> Motor neuron –> Effector
What % of nerve fibers in spinal cord are propriospinal fibers?
50%
What are propriospinal fibers?
Fibers that connect segments of the spinal cord
What do sensory neurons do?
Respond to stimuli, either external or from CNS
What do muscle spindles do?
Provide information about muscle length to the CNS or spine based on how stretched out they are. Found within muscles. Increased stretch = increased firing rate
What do Golgi tendon organs do?
Provide information about tension placed on muscles, found in tendons. Increased stretch = increase firing rate
How many times more/less numerous are interneurons than motor neurons?
30X More numerous
What are Renshaw cells?
A type of interneuron that passes inhibitory signals to surrounding motor neurons to “sharpen” the signal
What is a motor unit?
Single motor neuron and the muscle cells it synapses
What do alpha motor neurons do?
Enervate larger skeletal muscle fibers
What do gamma motor neurons do?
Enervate intrafusal fibers of muscle spindles
What is a monosynaptic reflex?
Reflex whose circuits have no interneurons. Sensory synapses directly with motor.
Ex.) Muscle stretch reflex
What is a polysynaptic reflex?
Reflex that has interneurons between sensory and motor neurons, allowing modulation and more complex responses.
Ex.) Flexor-Extensor reflex
How does a stretch reflex work?
- Muscle spindle fiber responds to stretch of muscle
- Sensory neuron travels to spinal cord where it synapses with a motor neuron
- Motor neuron causes contraction of stretched muscle
- Sensory neuron can also synapse with interneuron to cause inhibition of opposing muscle motor neuron
What is the physiological purpose of a stretch reflex?
Maintain posture while walking or standing
What is the diagnostic test of the stretch reflex?
Knee jerk reaction
How do alpha and gamma motor neurons work together?
Both skeletal muscles and muscle spindles will contract or relax together to maintain ratio of muscle to muscle spindle length. This allows tone to be maintained during muscle movement.
How does a golgi tendon reflex work?
- Organ detects increased tension on tendon
- Sensory neuron travels to spinal cord, to interneuron
- Interneuron causes inibition of muscle of the stretched tendon and activation of opposing muscle
What is the physiological purpose of a golgi tendon reflex?
Ensure smooth voluntary movements at onset and termination of muscle contraction by equalizing contractile force.
Synchronizes force of contractile units, distributing load.
How does a flexor-extensor reflex work?
- Cutaneous sensory neuron interacts with multiple interneurons
- Interneurons cause activation and inhibition of motor neurons to cause affected limb to retract and opposite limb to push away.
What are the layers of the ovary from outside to inside?
Germinal epithelium - squamous or cuboidal
Tunica albugenia - dense connective tissue capsule
Cortex - contains follicles, highly cellular
Medulla - highly vascularized, pathways for estrogens and progesterone, loose CT
Follicular/Granulosa cells
Surround oocyte, secrete estrogen
What does estrogen do in the ovary?
Proliferate granulosa cells
Mature follicles
Monthly development of endometrium
What stimulates follicles to mature?
Estrogen and Follicle Stimulating Hormone (FSH)
What triggers ovulation?
Luteinizing Hormone (LH)
What are the steps of follicle development?
- Primary follicle: primordial follicle –> unilaminar primary follicle –> multilaminar primary follicle
- Secondary (Antral) follicle
- Graafian (mature) follicle
What is a primordial follicle?
Found in superficial cortex
Oocyte surrounded by simple squamous epithelium
Prophase of first meiotic division
What is a Unilaminar primary follicle?
Begin at beginning of puberty
FSH stimulates process of follicular growth
Oocyte surrounded by simple cuboidal epithelium
What is a multilaminar primary follicle?
Aka growing follicle
Follicular cells proliferate
Oocyte surrounded by stratified cuboidal epithelium (granulosa)
Zona pellucida appears between oocyte and first layer of granulosa cells (glycoprotein coat that initates acrosome reaction)
Interstitial cells differentiate into theca folliculi
What is a secondary (antral) follicle?
Granulosa cells accumulate liquor folliculi creating a fluid filled antrum
Granulosa cells convert androgens into estradiol via aromatase
Theca folliculi becomes 2 layers: theca interna (endocrine tissue that secretes androgens) and theca externa (CT and smooth muscle)
What is a Graafian (mature) follicle?
Oocyte surrounded by several layers of granulosa cells - corona radiata
Oocyte protrudes into antrum suspended by cumulus oophorus
Pre-ovulatory follicle
One dominant follicle will undergo ovulation per cycle.
What does initial surge of LH during ovulation do?
Oocyte in mature follicle completes first meiotic division
Granulosa cells produce prostaglandins/hyaluronan, ovarian wall weakens
Mature follicle ruptures and releases ovum together with corona radiata
What does the follicle become after ovulation?
Corpus luteum
What do granulosa and theca cells do under control of LH?
Granulosa lutein cells secrete progesterone and estrogen
Theca lutein cells secrete androgens and progesterone
What happens to corpus luteum if pregnancy doesn’t happen?
Degenerates after 14 days.
No LH, cells stop producing steriods
Decreased progesterone leads to menstruation
Corpus albicans - dense CT scar
What is atresia?
When follicles fail to mature and die
Most follicles die this way
In post-menopausal ovary, most follicles are gone due to ovulation or atresia
What collects oocyte into oviduct?
Fimbria
Where is the oocyte fertilized?
Oviduct
What are the layers of the oviduct?
Folded mucosa - simple ciliated columnar epithelium
Muscularis - circular and longitudinal smooth muscle
Serosa
NO SUBMUCOSA
What are peg cells?
Cells in oviduct epithelium between ciliated cells that secrete factors that activate sperm and provide nutrition and protection for ovum and zygote
What are the four regions of the oviduct?
Infundibulum
Ampulla - fertilization usually occurs here
Isthmus
Intramural
Mucosa becomes less convoluted and muscularis becomes thicker as approach uterus
What are the layers of the uterus?
Muscularis - Myometrium
Mucosa - Endometrium
What does the myometrium contain?
3-4 layers of smooth muscle
Grows during pregnancy to cause contractions
Contains arcuate arteries to feed endometrium and myomesium
What does the endometrium contain?
Simple ciliated columnar epithelium with simple tubular glands
Thick lamina propria
Functionalis layer - thickens rapidly, shed during menstruation, progesterone sensitive
Basalis layer - closest to myometrium, remains after menstruation, contains bases of glands
What are the phases of the menstrual (ovarian) cycle?
- Menstrual (resting) phase - days 1-4, functionalis shed
- Proliferative (follicular) phase - days 5-14, functionalis reconstituted, stimulated by estrogen
- Ovulation
- Secretory (luteal) phase - days 15-28, glands secrete, maximum thickness of functionalis
What is the cervix?
Lower cylindrical part of the uterus
Wall of dense CT and smooth muscle
Epithelium depends on age and location
Endocervix - simple columnar mucus secreting epithelium with branched tubular glands
Stratified squamous epithelium meets columnar at squamo-columnar junction
How does the squamo-columnar junction change with age?
Exposure to vaginal environment can stimulate reprogramming of epithelial cells.
SCJ recedes from opening of cervix premenarch to top of cervix postmenopause
What is the transformation zone?
Columnar epithelium replaced by stratified squamous epithelium (metaplasia)
Site of most cervical cancers
What are nabothian cysts?
Overgrowth of stratified squamous epithelium that blocks glands. Not necessarily cancerous
What are the layers of the vagina?
Epithelium - stratified squamous, no glands
Lamina propria - elastic fibers
Muscularis - scattered smooth muscle
Adventitia - dense CT with elastic fibers
What are mammary glands?
Modified sweat glands - branched compound tubuloalveolar glands
Secretory portions in alveoli and alveolar ducts
Undergo marked changes during pregnancy and lactation under influence of Prolactin
What do the testis do?
Produce spermatozzoa and testosterone
What are the layers of the testis?
- Tunica albuginea - dence CT
- Mediastinum testis - divides testes into lobulues
- Seminiferous tubules - site of spermatogenesis
What are sertoli cells?
Form blood-testis barrier to prevent autoimmune attack
Tight junctions
What are leydig cells?
Produce androgens
In interstital tissue
Respond to LH
Why is there a blood-testis barrier?
Sperm were developed after immune system was, need to be separated
What are the intratesticular ducts?
Tubes that carry spermatozoa and liquid from seminiferous tubules to the duct of the epididymis
Tubuli Recti
Rete Testis - simple cuboidal
Ductuli efferentes - scalloped/festooned epithelium
What is the epididymis
Connects ducti efferentes to ductus deferens
Sperm undergo final maturation here
Single tubule, 4-5 meters long
Pseudostratified columnar epithelium
What is the ductus deferens?
Aka vas deferens
Connects epididymis to urethra
Site of vasectomy
Pseudostratified columnar with thick muscularis
Which are the accessory glands and what do they do?
Seminal vesicle - 70% of ejaculate, fructose, prostaglandins, fibrinogen
Bulbourethral glands - release clear mucus like secretion to coat urethra
What are the layers of the prostate gland?
Periopheral zone - main glands, primary area of prostate cancer
Central zone - submucosal glands
Transition zone - around urethra, mucosal glands, site of benign prostatic hypertrophy
What is corpora amylacea?
Concretions of stuff. Identify prostate from mammary and salivary glands
What are the parts of a sperm cell?
Acrosome - enzymes to break down outer layer of ovum
Head - contains nucleus
Axoneme - contains centriole and and cytoskeletal components
Tail - flagella
Cell membrane has chemotactic sensors to give it direction - gradient sensing
What are steps of spermatogenesis
Spermatogonia divide to replace themselves AND undergo meiosis to create sperm
- Spermatogonia (2n)
- Primary spermatocyte (2n) –> Meiosis 1
- 2 Secondary spermatocytes (1n) –> Meiosis 2
- 4 Spermatids (1n)
How long does spermatogenesis take?
64 days
What does inhibin do?
Produced by sertoli cells
Negative feedback in excess FSH secretion
What does gonadotrophin releasing hormone do?
Released from hypothalamus
Causes release of LH and FSH
What does Leutinizing hormone do?
Stimulates Leydig cells to secrete testosterone
What does Follicle Stimulating Hormone do?
Stimulates Sertoli cells to form estrogens from testosterone
What does testosterone do?
Secreted by leydig cells
drives division of spermatogonia
What does estrogen do?
Formed from testosterone by sertoli cells
Regulators of spermatogenesis
How many sperm do both testis make per day?
120 million, most waiting in the vas Deferens
Where does each part of the ejaculate come from?
- Seminiferous tubules - 5% of product
- Seminal vesicles - 60-70%
- Prostate gland - 25-30%
- Bulbourethral glands - 1%
What does the prostate gland add to the ejaculate
- Clotting enzymes
- Pro-fibrinolysin (plasminogen)
- Various alkaloids
What is the optimal pH for sperm function?
6.5
What is clinically important about Bulbourethral (Cowper’s) secretion?
Can cause pregnancy
Can transfer disease
What is in semen?
Secretions from seminal vesicles, prostate, cowper’s glands
Contains fuel, alkaloids to regulate pH, clotting factors, clot removing factors
pH 7.5
Prostate fluid gives milky appearance
How long can sperm survive in utero?
2-3 days
What is sperm capacitation?
Semen contains inhibiting factors to keep sperm from moving
Inhibition washed away upon entry into vagina
Acrosome weakens
Ca2+ permeability increases
How does erection happen?
Parasympathetic innervation, in response to physiological and psychological factors
ACh, NO and others cause vasodilation
Corpora cavernosa and corpus spongiosum fill with blood
What is the process of ejaculation?
Emission
1. Sympathetic impulses from reflex centers in spine (T12-L2) cause contractions of vas deferens
2. Once ejaculate enters urethra it has mixed with seminal vesicle and prostate secretions
Ejaculation
3. Contraction of ischiocavernosus and bulbospongiosus muscles cause expulsion of semen
Where is inhibin B made and what does it do?
Made in granulosa cells of ovaries, inhibits FSH secretion
What are the 3 natural estrogens?
Estradiol (E2) - predominant in reproductive years
Estrone (E1) - predominant in menopause
Estriol (E3) - predominant in pregnancy
What does estrogen do?
Female sexual maturation Increase CNS excitability Stimulate endometrial proliferation and uterine growth Maintain blood vessels and skin Reduce rate of bone readsorption Cardio protective Enhance blood coagulability
Hormonal changes during menstrual cycle
- Estrogen increases before ovulation, which decreases FSH and LH
- Estrogen reaches threshold, causes LH surge right before ovulation
- After ovulation, Estrogen decreases, Progesterone increases, drops off before mense.
- Increases of LH and FSH at menstruation
What does LH do in women?
Stimulates Theca interna to create estrogen and androgens
Stimulates Granulosa cells to create inhibin B
What does FSH do?
Stimulates Granulosa cells to create inhibin B
What do androgens do?
Stimulate Granulosa cells to create inhibin B
Menstrual cycle hormones
- Estrogen is at low point during menses, pituitary secretes FSH, LH
- FSH, LH stimulate growth of preovulatory ovarian follicles
- E2 increase inhibits FSH and LH creating a dominant folllicle
- FSH and LH accumulate in anterior pituitary due to E2
- LH surge causes ovulation
- Luteal phase begins at ovulation, corpus luteum releases progesterone
- Progesterone prevents second ovulation
- If no fertilization, corpus luteum becomes corpus albicans
What causes LH surge?
E2 levels reach threshold, flip from negative feedback to positive, causing LH and FSH stored up to be releaased
What does progesterone do?
Progestational - prepares uterus Increases fat deposition Decreases CNS excitability Increases insulin levels Increases aldosterone Increases body temperature Decreases PCO2 during pregnancy
HPO axis in childhood
Leptin levels build at pregnancy to level causing release of GnRH
Leptin is what also causes athletes or anorexic women to stop their cycles. Based more on weight than age
HPO axis at puberty
Increase estrogen secretion begin sexual development and menarch. Ovulation begins 2-4 years past first mense
HPO axis at perimenopause
Fluctuation of gonadotropins, may be from loss of inhibins
HPO axis at menopause
Decline of E2 estradiol
FSH levels markedly elevated at onset of menopause
Usually around 50 yrs old
Estrone E1 is predominant
Ovaries no longer secrete progesterone and estradiol
Aromatization of adrostenedione in adrenal glands and adipocytes is source of E1
Events of early pregnancy (month 1-2)
- Trophoblast releases human chorionic gonadotropin (hCG)
2. hCG bypasses HPO axis control, prompts corpus luteum to continue expressing estrogens and progesterone
Evens of pregnancy (months 2-3)
- Placenta takes over production of progesterone and estrogen by 8 weeks
- Corpus luteum degenerates and ovaries become inactive until after childbirth. If placental hormones are inadequate, endometrium degenerates and pregnancy is aborted
- Progesterone prevents uterine contractions, moderates maternal immune response and stimulates development of mammary glands
Parturition (birth) hormones
Estrogen - induces uterine oxytocin receptor expression
Oxytocin - causes contractions via positive feedback
Relaxin - peptide hormone that causes relaxation of cervix and pelvic ligaments
Predominant inhibitory control of prolactin
Prolactin inhibitory factor (dopamine) produced continuously by hypothalamus to suppress prolactin until needed.
Lactation
Prolactin stimulates mammary glands to produce milk after birth
Colostrum - first milk, yellow and thick, has antibodies, laxative effect
Dental visits during pregnancy
Oral infections such as gum disease linked to preterm birth
Fetal organ development occurs during first trimester, dental work should be put off till 2nd trimester
