MCAT Study Guide Biology Ch. 12 – Reproduction 2017-08-15T06:45:06+00:00

I.          12.1:  THE MALE REPRODUCTIVE SYSTEM

A.     ANATOMY

1.     Testes – two roles include spermatogenesis and secretion of sex hormones

2.     Seminiferous tubules – site of spermatogenesis, in the testes

a)     Sustenacular (sertoli) cells – cells that line the seminiferous tubules and nuture and protect the developing sperm

3.     Interstitial (Leydig) cells – cells found in the testicular interstitium and produce testosterone

4.     Epididymis – long coiled tube on the posterior testicle that the seminiferous tubules empty into

5.     Vas (ductus) deferens – leads from epididymis to the urethra (has to travel through the inguinal canal, around the bladder where it joins the seminal vesicle to form the ejaculatory duct)

6.     Seminal vesicles – pair of glands on the posterior surface of the bladder and secrete the majority of volume (60%) of semen (mostly fructose)

7.     Prostate gland – secretes fructose and coagulant (35% semen volume)

8.     Bulbourethral glands – secrete thick, alkaline mucous to lubricate urethra and neutralize acids in male urethra and vagina

B.     THE MALE SEXUAL ACT

1.     Arousal – dependent on parasympathetic nervous input

a)     Erection – dilation of arteries supplying erectile tissue

b)     Lubrication – bulbourethral glands secrete thick mucous which serves as lubricant

2.     Orgasm – stimulation by sympathetic NS

a)     Emission – propulsion of sperm from the (vas deferens) and semen into the urethra

b)     Ejaculation – propulsion of semen out of urethra (reflex reaction to presence of semen in urethra)

3.     Resolution – return to normal state

 

II.          12.2:  SPERMATOGENESIS

A.     SPERM PRECURSORS

1.     Spermatogonium – first cell, diploid (2N); replicates DNA

2.     Primary spermatocyte – diploid (2N), goes through meiosis I

3.     Secondary spermatocytes – (N), goes through meiosis II

4.     Spermatid – (N), immature sperm

5.     Spermatozoan – mature sperm

B.     HORMONAL CONTROL OF SPERMATOGENESIS

1.     Testosterone – stimulates division of spermatogonia

2.     LH – stimulates interstitial cells to secrete testosterone

3.     FSH – stimulates sustenacular cells

4.     Inhibin – secreted by sustenacular cells, inhibits FSH (negative feedback)

 

III.          12.3:  DEVELOPMENT OF THE MALE REPRODUCTIVE SYSTEM

A.     Embryo has both Wolffian ducts and Mullerian ducts:

1.     Wolffian ducts – develop into male internal genitalia

2.     Mullerian ducts – develop into female internal genitalia (occurs by default)

B.     Mullerian inhibiting factor (MIF)

Produced by testes and causes regression of Mullerian ducts and prevention of formation of female internal genitalia

C.    Testosterone

Secreted by cells that will later give rise to testes (formation begins around week 7); responsible for formation of male external genitalia

D.    Dihydrotestosterone

Converted from testosterone, this is responsible for the development of male external genitalia

 

IV.          12.4:  ANDROGENS AND ESTROGENS

A.     Testosterone production falls after birth and does not rise again until puberty

B.     Estrogen is analogous to testosterone

C.    GnRH

Secreted by the hypothalamus to stimulate FSH and LH, ultimately controls sex steroid production during puberty and adulthood

D.    Men:

1.     LH – acts in interstitaL cells to stimulate testosterone

2.     FSH – stimulate Sustenacular cells

E.     Women:

1.     LH – stimulates formation of corpus Luteum and progesterone

2.     FSH – stimulates granulosa cells to secrete estrogen

V.          12.5:  FEMALE REPRODUCTIVE SYSTEM

A.     ANATOMY AND DEVELOPMENT

1.     Internal genitalia are derived from the Mullerian ducts; these develop in the absence of testosterone (no estrogen necessary)

 

VI.          12.6: OOGENESIS AND OVULATION

A.     OOGENESIS

1.     Oogenesis begins prentally; oogonia undergo mitosis in utero and enter first phase of meisos and arrest in prophase I as primary oocytes

a)     Primary oocytes are surrounded by granulosa cells (everything is the follicle); granulosa cells produce estrogen

b)     Primordial follicle – immature primary oocyte and surrounding cells (as it matures, the mucopolysaccharide layer

[zona pellucida] forms around it)

c)     Thecal cells – analogous to the testicular interstitial cells, respond to LH

2.     There is progressive loss of cells until there are only about 2 million cells, and by puberty this number is reduced to 400,000

3.     Only about 400 oocytes are ever actually ovulated; the remainder degenerate

B.     OVULATION

1.     Hormonal changes stimulate completion of first meiotic division and ovulation, yielding a secondary oocyte and small polar body (contains ½ the DNA, but no cytoplasm/organelles)

a)     Graafian follicle – mature follicle that bursts during ovulation (many are maturing, but only one progresses to the point of ovulation; others degenerate)

b)     The secondary oocyte is arrested in metaphase II

c)     The secondary oocyte is released, now called the corona radiata

2.     The second meiotic division occurs only if the secondary oocyte is fertilized

a)     This division leads to an ovum and secondary polar body; once the secondary oocyte releases the second polar body the ovum matures into an ootid then an ovum

b)     Once the ovum is mature, the sperm and ovum fuse and a diploid zygote is formed

 

VII.          12.7:  THE MENSTRUAL CYCLE

A.     OVARIAN CYCLE

1.     Follicular phase – about 13 days

a)     Primary follicle matures and secretes estrogen

b)     FSH stimulates follicular maturation

2.     Ovulatory phase  – on about day 14

a)     Surge of LH triggers release of secondary oocyte is released from ovary

b)     LH also causes follicle remnants to become the corpus luteum

3.     Luteal phase – about 14 days

a)     Begins with full formation of corpus luteum, which secretes estrogen and progesterone

B.     UTERINE CYCLE

1.     Menstruation – about 5 days

a)     Triggered by the degeneration of the corpus luteum and subsequent drop in estrogen and progesterone levels

2.     Proliferative phase – about 9 days

a)     Estrogen produced by the follicle induces the proliferation of the new endometrium

3.     Secretory phase – about 14 days

a)     Estrogen and progesterone secreted by the corpus luteum further increase development of the endometrium

C.    FOCUS ON THE HORMONES

1.     GnRH from hypothalamus stimulates FSH and LH release from anterior pituitary

2.     FSH helps the granulosa and thecal cells develop during the follicular phase and secrete estrogen

3.     Lower levels of estrogen inhibit GnRH, FSH, and LH, but as it increases, it stimulates LH

4.     This sudden surge in LH causes ovulation, LH stimulates the corpus luteum secretes estrogen and progesterone

5.     Estrogen and progesterone inhibit GnRH, FSH, and LH

 

VIII.          12.8:  HORMONAL CHANGES DURING PREGNANCY

A.

Endometrium is shed due to decrease in estrogen/progesterone (degenerating corpus luteum)

B.

Corpus luteum degenerates due to decrease in LH (which is inhibited by high estrogen/progesterone)

C.

Pregnancy keeps progesterone/estrogen levels continually high, which prevents ovulation each month by preventing LH surge

D.

If pregnancy occurs, hCG replaces LH and maintains the corpus luteum, thereby maintaining high estrogen/progesterone levels and preventing endometrial degeneration

 

IX.         12.9:  FERTILIZATION AND CLEAVAGE

A.

Secondary oocyte (surrounded by the corona radiata and zona pellucida) enter the uterine tube

B.

Fertilization usually occurs in the uterine tube; sperm must penetrate the corona radiata and bind to and penetrate the zona pellucida

1.     Acrosome – large vesicle in sperm head containing hydrolytic enzymes released by exocytosis; and acrosomal process (actin) elongates towards the zona pellucida and binds to it

2.     About 20 minutes after sperm and egg fuse, the secondary oocyte completes meiosis II, giving rise to an ootid and second polar body

3.     Ootid matures rapidly, becoming an ovum, then the sperm and egg nuclei fuse, becoming a zygote

4.     Fast and slow block to polyspermy – egg plasma membrane depolarizes which prevents other sperm from fusing after the first one; the slow block causes hardening of the zona pellucida

C.    CLEAVAGE

1.     Cleavage – the first stage in embryogenesis; cell division without growth

a)     Morula – ball of up to 16 cells

2.     Morula → blastocyte (ring of cells called trophoblast, surrounding the inner cell mass)

3.     Trophoblast will give rise to the chorion, inner cell mass becomes the embryo

 

X.          12.10:  IMPLANTATION AND THE PLACENTA

A.

Blastocyte reaches the uterus and implants about 1 week after fertilization; sinks into and is surrounded by the endometrium, absorbing nutrients

B.

Placenta takes about 3 months to develop, so hCG is necessary for maintenance of endometrium until then

C.    Placental villi

horionic projections (from trophoblast) extend into endometrium, where fetal capillaries will grow; maternal blood fills the sinuses between the villi

D.    Inner cell mass produces 4 structures:

1.     Embryo

2.     Amnion – sac surrounding the embryo and amniotic fluid (formed after the chorion)

3.     Yolk sac – first site of RBC synthesis in the embryo

4.     Allantois – develops from embryonic gut, forms blood vessels of the umbilical cord

XI.          12.11:  POST-IMPLANTATION DEVELOPMENT

A.     Gastrulation

Next phase of embryogenesis where the 3 primary germ layers (ectoderm, mesoderm, and endoderm) become distinct

Ectoderm Mesoderm Endoderm
●       Nervous system●       Pituitary, adrenal medulla●       Cornea, lens

●       Epidermis of skin (hair, nails, sweat)

●       Oral, nasal, anal epithelium

●       what is attractive – skin, hair, eyes, brain

●       All muscle, bone, CT●       Entire CV system and blood●       Lymphatic system

●       Urogenital organs

●       Dermis of skin

●       Everything in the middle

●       GI tract epithelium●       GI glands●       Respiratory epithelium

●       Epithelium of urogenital tract

●       Urinary bladder

●       Internal tubing

B.     Neurulation

Formation of the nervous system; the invagination and pinching off of a layer of ectoderm on the dorsum forms the dorsal neural groove, which gives rise to the neural tube

1.     The neural tube turns into the brain and spinal cord under instruction from the underlying notochord (from the mesoderm)

C.    Fetus

After 8 weeks when all major organ systems are present

 

XII.          12.12:  DIFFERENTIATION

A.     Totipotent cells

Primitive (stem) cells in an early embryo that have potential to become any cell type

B.     Determination

A point in time in which the cell fate and development has become fixed; can be induced by a cell’s environment or be preprogrammed

C.    Differentiation

Specialization of any type of cell during development

D.    Dedifferentiation

Process in which a specialized cell becomes unspecialized

 

XIII.          12.13:  BIRTH AND LACTATION

A.     Partuition – birth

B.     Milk production

Inhibited by estrogen and progesterone; after birth these hormone levels drop and mild production begins

 

  1. ELISA (Enzyme-linked immuno-sorbent assay)
    • Detects presence of either antigens or antibodies
    • Used to screen people for viral infections
  2. RIA (Radioimmunoassay)
    • Use radiolabeled antibodies rather than enzyme-linked antibodies
    • Used to measure the relative amounts of hormones or drugs in serum
  3. Electrophoresis
    • Separating things by size or charge
  4. Blotting
    • Southern blot
      • Detects specific DNA sequences
    • Northern blot
      • RNA
    • Western blot
      • Proteins
  5. Recombinant DNA
    1. Combines DNA from two organisms (ex:  bacteria with insulin DNA inserted into plasmid)
  6. PCR (polymerase chain reaction)
    1. Detects and amplifies specific DNA sequences
  7. DNA sequencing

MCAT Study Guide Biology - Kim Matsumoto


More MCAT Study Guide Biology

1.

Ch. 2 Thermodynamics and Cellular Respiration

2.

Ch. 3 Transcription + Translation

3.

Ch. 4 Microbiology

4.

Ch. 5 Cell Biology

5.

Ch. 6 Genetics

6.

Ch. 7 Nervous System

7.

Ch. 8 Circulatory System

8.

Ch. 9 Renal + Digestive System

9.

Ch. 10 Musculoskeletal System

10.

Ch. 11 Respiratory System

11.

Ch. 12 Reproductive System

← View Full MCAT Study Guide Directory