Human Biology: Muscular, Reproductive, Cellular, and Protein Synthesis Review

Comprehensive Question and Answer flashcards derived from the lecture transcript covering muscle histology, sliding filament theory, cell division, human reproduction, embryonic development, contraception, STIs, and protein synthesis.

What are the three types of muscle tissue found in the body?

Cardiac muscle, smooth muscle, and skeletal muscle.

What structural and operational features characterize cardiac muscle tissue?

Cardiac muscle is found in the heart, has branched and striated fibers, typically contains one nucleus (some have two), features intercalated discs at fiber ends to aid wave-like contractions, and is under involuntary control.

What are the structural features and locations of smooth muscle?

Smooth muscle lacks striations, is spindle-shaped with one single nucleus, is under involuntary control, and is located in the lining of the digestive system, bladder, veins, arteries, and the iris.

What are the four primary functional characteristics of muscle tissue?

Extensibility (ability to stretch/extend), elasticity (ability to retract back to starting length), excitability (ability to be stimulated), and contractility (ability to contract).

What is the difference between the origin and insertion of a skeletal muscle?

The origin attaches to a fixed part of the bone, while the insertion attaches to the bone that will move.

What roles do agonist and antagonist muscles play during a movement?

The agonist is the main muscle performing the work, while the antagonist supports the agonist or produces the opposite action to help maintain positions.

How do thin and thick filaments interact during the sliding filament model of contraction?

Actin (thin) and myosin (thick) do not shorten. Bound ATP on the myosin head hydrolyzes into ADP and phosphate. The myosin head forms a cross bridge with actin, executes a power stroke releasing ADP and phosphate to pull actin toward the center, and detaches when a new ATP molecule binds.

How do tropomyosin, troponin, and calcium regulate muscle contraction?

Tropomyosin blocks myosin binding sites on actin, held by troponin. When calcium is released, it binds to troponin, causing troponin to change shape and move tropomyosin off the myosin binding sites, allowing contraction.

How do chromosome and chromatid counts change in a human cell before and after interphase?

Before interphase, the cell has $46$ chromosomes and $46$ chromatids. After interphase replication, it has $46$ chromosomes and $92$ chromatids.

What key structural events occur during Prophase of mitosis?

Centrioles become visible and radiate microtubules, the nucleus and nuclear membrane break down, chromatin threads coil into visible chromosomes (each with two chromatids joined at a centromere), and microtubules form the spindle.

How does cytokinesis divide an animal cell following mitosis?

A furrow develops in the cytoplasm between the two nuclei, deepens, and cuts the cytoplasm into two, producing two distinct daughter cells.

What occurs during Prophase I of meiosis that creates genetic variety?

Homologous chromosomes pair up and undergo crossing over, exchanging genetic information to produce recombinant chromosomes.

How does chromosome alignment differ between Metaphase I and Metaphase II of meiosis?

In Metaphase I, chromosomes line up along the middle in homologous pairs. In Metaphase II, chromosomes line up in a single file line.

What is the final cellular outcome of meiosis?

Four non-identical haploid cells, each containing $23$ chromosomes.

What is the function of the scrotum in male reproductive anatomy?

It holds the testicles outside the main body cavity to maintain the lower temperature necessary for proper spermatogenesis.

What are the roles of the seminal vesicles, prostate gland, and bulbourethral glands?

Seminal vesicles produce $60\text{\%}$ of semen volume (yellowish, alkaline fluid to nourish/transport sperm); the prostate gland contracts during ejaculation to contribute citric acid and a liquifying enzyme; bulbourethral glands secrete clear mucus to clear acidic urine from the urethra.

What is the full developmental sequence and chromosome count of spermatogenesis?

Spermatogonium ($46$) $\rightarrow$ Primary spermatocyte ($46$) $\rightarrow$ Secondary spermatocytes ($23$) $\rightarrow$ Spermatids ($23$) $\rightarrow$ Spermatozoa ($23$).

How long does spermatogenesis take from spermatogonium to mature spermatozoon?

Approximately $72\,\text{days}$.

What are the main structural regions of a mature sperm cell and their functions?

The head contains the haploid nucleus ($23$ chromosomes) and acrosome (digestive enzymes); the neck contains a centriole; the middle piece contains mitochondria for ATP energy production; and the tail/flagellum provides contractile movements for propulsion.

What is the role of Sertoli cells in the seminiferous tubules?

Sertoli cells support and nourish developing sperm cells.

What is the complete developmental sequence and chromosome count of oogenesis?

Oogonium ($46$) $\rightarrow$ Primary oocyte ($46$) $\rightarrow$ Secondary oocyte ($23$) $\rightarrow$ Ootid ($23$) $\rightarrow$ Ovum ($23$).

Why are polar bodies formed during oogenesis?

Unequal cytoplasmic division during meiosis produces polar bodies with very little cytoplasm, allowing the functional ovum to retain almost all cytoplasm, nutrients, and organelles required for early development.

What are the developmental stages of an ovarian follicle prior to ovulation?

Primary follicle $\rightarrow$ Secondary follicle (develops a fluid-filled antrum) $\rightarrow$ Graafian follicle (mature follicle near ovary surface).

What hormonal event triggers ovulation, and when does it typically occur?

A high level of oestrogen causes a surge in luteinizing hormone (LH), triggering the release of the secondary oocyte at around day $14$ of a typical $28\,\text{day}$ cycle.

What is the role of the corpus luteum following ovulation?

It develops from the ruptured empty follicle and secretes progesterone and oestrogen to maintain the endometrium for potential implantation.

What are the five phases of the menstrual cycle and their general timing?

Menstruation (Days $1$ to $4$), Proliferative phase (Days $5$ to $12$), Ovulation (Days $13$ to $15$), Secretory phase (Days $16$ to $20$), and Premenstrual phase (Days $21$ to $28$).

What volume of semen is typically released during ejaculation?

Approximately $3\,\text{mL}$.

What two protective layers surround a secondary oocyte?

The corona radiata (outer layer of follicular cells) and the zona pellucida (inner glycoprotein layer).

What is the function of the acrosomal reaction during fertilisation?

The acrosome releases digestive enzymes that break down the corona radiata and zona pellucida so the sperm can reach and fuse with the oocyte plasma membrane.

What is the correct sequence of early embryonic development from fertilisation to implantation?

Zygote $\rightarrow$ Cleavage $\rightarrow$ Ball of cells $\rightarrow$ Blastocyst $\rightarrow$ Implantation.

What are the two structural parts of a blastocyst and their functions?

The inner cell mass (develops into the embryo) and the trophoblast (outer layer that assists in implantation and nutrient exchange).

What function does human chorionic gonadotropin (hCG) serve in early pregnancy?

hCG is produced by the blastocyst to maintain the corpus luteum, ensuring continuous production of progesterone and oestrogen for $8$ to $12\,\text{weeks}$ to prevent menstruation.

What four embryonic membranes develop to protect and support the embryo?

The amnion, chorion, yolk sac, and allantois.

What blood vessels are contained in the umbilical cord and what are their functions?

Two umbilical arteries carry deoxygenated blood and wastes from the foetus to the placenta, and one umbilical vein carries oxygen and nutrients from the placenta to the foetus.

At what stage of development is the embryo officially called a foetus?

By the end of $8\,\text{weeks}$ (or after the second month) of pregnancy, once major body systems and structures have formed.

What events define the three stages of labour?

First stage: uterine contractions cause cervical dilation to approximately $10\,\text{cm}$; Second stage: delivery of the baby through the birth canal; Third stage: delivery of the placenta and remaining membranes (afterbirth).

What are the three special circulatory shunts in the foetus before birth?

The ductus venosus (bypasses the liver), ductus arteriosus (connects pulmonary artery to aorta, bypassing the lungs), and foramen ovale (opening between right and left atria).

How does the foramen ovale close at birth?

With the first breath, blood flow to the lungs increases, raising pressure in the left atrium which pushes the tissue flap over the foramen ovale closed.

What four techniques are used in natural fertility awareness methods?

Rhythm method, temperature method, cervical mucus method, and the symptothermal method.

Under what conditions is lactational amenorrhoea effective as a contraceptive option?

When the mother is exclusively breastfeeding, menstruation has not returned, and the baby is under $6\,\text{months}$ old.

How do combined oral contraceptive pills differ from mini-pills?

Combined pills contain oestrogen and progestogen to prevent ovulation, alter cervical mucus, and change the endometrium. Mini-pills contain progestogen only, primarily thickening cervical mucus and altering the uterine lining.

What surgical procedures are performed for male and female sterilisation?

Vasectomy in males (cutting/blocking vas deferens) and tubal ligation in females (cutting, sealing, or blocking fallopian tubes).

What bacterium causes Chlamydia, and what serious condition can it cause in untreated females?

Caused by Chlamydia trachomatis, untreated infection in females can cause pelvic inflammatory disease (PID), ectopic pregnancy, and potential infertility.

What are the four clinical stages of a Syphilis infection?

Primary stage (painless chancre sore), Secondary stage (skin rash, fever, sores), Latent stage (asymptomatic period), and Tertiary stage (severe damage to brain, heart, and nervous system).

Which specific immune cells are targeted and damaged by HIV?

T-helper lymphocytes.

What pathogen causes Trichomoniasis?

The protozoan Trichomonas vaginalis.

What are the two main stages of protein synthesis and where do they occur?

Transcription occurs in the nucleus (DNA to mRNA), and Translation occurs at ribosomes in the cytoplasm (mRNA to protein).

What are three chemical and structural differences between RNA and DNA?

RNA contains ribose sugar instead of deoxyribose, is usually single-stranded instead of double-stranded, and contains the base uracil (U) instead of thymine (T).

What base pairing rules apply when RNA polymerase synthesizes mRNA from a DNA template strand?

$A \rightarrow U$, $T \rightarrow A$, $C \rightarrow G$, and $G \rightarrow C$.

What is the functional difference between a codon and an anticodon?

A codon is a three-base sequence on mRNA that specifies an amino acid or start/stop signal. An anticodon is a complementary three-base sequence on a tRNA molecule that carries a specific amino acid.