Sperm and Sperm Development

Question 1

sperm

Answer 1

consists of a rounded head containing the acrosome, a connecting piece called the centriole, and a long thin tail

Question 2

sperm head

Answer 2

composed of the nucleus and the acrosome
- nucleus contains genetic material and the acrosome is a unique organelle responsible for the penetration of the oocyte during fertilization

Question 3

sperm centriole

Answer 3

links the head to the tail
connecting piece consists of two centrioles

Question 4

sperm tail

Answer 4

divided into three parts: the midpiece, the principle piece (bulk of the tail), and the end piece
- midpiece contains mitochondria, the main energy source of the sperm

Question 5

microstructure of the sperm: head region

Answer 5

head of the sperm contains specialized proteins and enzymes responsible for facilitating fertilization
- proteins are exocytosed and released during the acrosome reaction
perinuclear theca is the protein layer between the acrosome and nuclues, which is then further divided into the sub-acrosomal layer and the post-acrosomal sheath

Question 6

sub-acrosomal layer

Answer 6

found between the inner acrosomal membrane and the nuclear envelope
- it is continuous with the outer periacrosomal layer, which is sandwiched between the plasma membrane and the outer acrosomal membrane that overlies the equatorial segment

Question 7

equatorial segment

Answer 7

thought to have distinctive and essential functions in the intimate interactions between sperm and egg fertilization

Question 8

post-acrosomal sheath

Answer 8

begins at the end of the acrosome and is between the plasma membrane and the nuclear envelope
- the surface groove marks the end of the perinuclear theca

Question 9

acrosome reaction

Answer 9

the exocytosis of the acrosome, which functions to penetrate the zona pelucida of the ovulated oocyte for fertilization
- hydrolytic enzymes are responsible for fertilization and are stored in the acrosome

Question 10

sperm tail microtubules

Answer 10

the tail has distinctive organization of microtubules and fibrous sheaths. microtubules have 9 peropheral doublets and two central singlets. there are radial spokes between the microtubules

Question 11

sperm tail fibrous sheath

Answer 11

the fibrous sheath is located around the circumference of the tail and inserts on two of the peripheral doublet columns

Question 12

spermatogenesis

Answer 12

1. spermatogonia are diploid somatic cells that divide by mitosis to initiate spermatogenesis. these cells lie of the basal lamina
2. primary spermatocytes are diploid cells formed by mitosis of spermatogonia. these cells arrest in prophase of meiosis I
3. secondary spermatocytes are haploid cells formed by first meiotic division of primary spermatocytes. these cells are located closer to the lumen and they quickly complete the second meiotic division
4. spermatids are haploid cells formed by the second mitotic division of secondary spermatocytes. these cells are adjacent to the lumen, and they do not divide, but do undergo differentiation. they transform from spherical cells to elongated cells
5. spermatozoa are haploid cells formed by the differentiation of spermatids. these cells are released from the seminiferous epithelium by the Sertoli cells and lie free in the lumen of the convoluted portions of the seminiferous tubules

Question 13

development of mature sperm

Answer 13

takes place in two steps: spermatogenesis: process by which spermatogonia develop into spermatid spermiogenesis: process of differentiation of spermatids. this is a constant process that occurs at fixed intervals. a cycle begins every 16 days and lasts for ~60 days

Question 14

timeline for sperm development

Answer 14

16 days: mitosis
24 days: meiosis I and II
24 days: spermiogenesis

Question 15

16 days: mitosis

Answer 15

spermatogonia lie on the basal lamina of the seminiferous tubule
- they divide by mitosis to form more spermatogonia or to form primary spermatocytes in spermatocytogenesis

Question 16

24 days: meiosis I and II

Answer 16

meiosis is a 2 division process where diploid primary spermatocytes divide into haploid secondary spermatocytes (meiosis I)

secondary spermatocytes divide by meiosis II to form haploid spermatids
- this stage lasts a few hours

Question 17

24 days: spermiogenesis

Answer 17

no cell division occurs during spermiogenesis
spermatids undergo differentiate where early spermatids are transformed into late spermatids
- early spermatids remain connected to each other by cytoplasmic bridges, which are a result of incomplete cell division and allow for maturation synchronously into late spermatids

Question 18

spermatid differentiation steps

Answer 18

1. the acrosome develops and covers the dense, elongated nucleus
2. the flagellum grows out fo the pole opposite the acrosome. develops from centrioles of the spermatid and grows towards the lumen
3. mitochondria become arranged around the flagellum
4. majority of the cytoplasm is cast off as a residual body leaving only a thin layer of cytoplasm around the nucleus. Sertoli cells consume the residual body

Question 19

spermiation

Answer 19

late spermatids are released into the lumen of the convoluted portion of the seminiferous tubule as spermatozoa
- spermiation is the process of releasing late spermatids as spermatozoa from the Sertoli cells into the lumen

Question 20

sperm maturation

Answer 20

the final maturation of sperm occurs in the epididymis, where cells gain the ability to move
- they gain the ability to fertilize the egg through capacitation, which occurs in the female reproductive tract

Question 21

capacitation

Answer 21

process that functions to destabilize the sperm acrosome and increase the motility of the sperm tail
- once in the female reproductive tract, the acrosome reaction can take place and fertilization can occur