📚 Question Bank

The movement of the thyroid gland with deglutition is due to the attachment of Berry's ligament to the cricoid cartilage.

Ligament of Berry:

The pretracheal fascia encloses the thyroid gland to form its false capsule. This capsule is thickened posteriorly and on either side forms a suspensory ligament which is known as ligament of Berry or lateral thyroid ligament. The posteromedial aspects of the lobes of the thyroid are attached to the side of the cricoid cartilage by the ligament of Berry. It also prevents the thyroid gland from sinking into the mediastinum.

The structure that is not damaged during the emergency tracheostomy is the inferior thyroid artery, as it is not a mid-line structure.

Isthmus, arteria thyroid ima, inferior thyroid vein are in the midline and are prone to damage during tracheostomy.

The newly discovered salivary glands are predominantly present over torus tubarius. Torus tubarius is the anatomical structure formed by the cartilage that supports the entrance of the auditory tube.

The proposed name of these newly identified glands is tubarial salivary glands. These glands extend caudally to the pharyngeal wall and cranially to Rosenmuller's fossa.

Positron emission tomography/computed tomography with radio-labeled ligands to the

prostate-specific membrane antigen (PSMA PET/CT) can visualize these salivary glands with high sensitivity and specificity.

Clinical significance:

It has been reported that radiotherapy over the location of these glands has led to xerostomia and dysphagia. Sparing these glands, thus, might improve the quality of life of patients receiving radiotherapy.

The anterior 2/3rds of the tongue is demarcated from the posterior 1/3rd by the terminal sulcus, also known as the sulcus terminalis.

Sulcus terminalis divides the tongue into anterior and posterior parts. The anterior or the oral part faces superiorly and the posterior or the pharyngeal part faces posteriorly.

Option A: Sigmoid sulcus is present on the mastoid surface of the temporal bone

Option B: Gingival sulcus is present between the tooth and the surrounding gingival tissue Option D: Median sulcus is the central sulcus present on the tongue

The structure marked A shows the foliate papillae which lie bilaterally on either side of the tongue near the sulcus terminalis.

Location of papillae in the tongue:

• Filiform papillae - They are minute cylindrical or conical projections that are mainly present on the dorsal part of the anterior 2/3rd of the tongue.
• Fungiform papillae - They are large, rounded and red in colour and are mainly present on the lingual margins and also on the dorsal surface of the tongue.
• Foliate papillae - They are red, leaf-like mucosal ridges that are present bilaterally in two
• zones at the sides of the tongue near the sulcus terminalis.
• Circumvallate papillae - They are large cylindrical structures that are around 8-12 in number.
• They are arranged in a V-shaped row immediately in front of the sulcus terminalis (not on the sides of the tongue).

The given image shows tongue deviation to the left, and the left genioglossus muscle is paralyzed in the above given clinical scenario.

Actions of genioglossus muscle:

• When both the right and left genioglossi contract, they protrude the anterior part of the tongue out of the mouth in the midline. When only one muscle contracts, it protrudes and pushes the tongue to the opposite side.
• It depresses the central part of the tongue.
• It is supplied by the hypoglossal nerve.

In conditions affecting the hypoglossal nerve, the genioglossus muscle on that side is paralyzed. In such cases, when the patient protrudes the tongue, it deviates towards the affected side due to the

muscle contraction on the normal side.

The genioglossi are attached to the genial tubercle present on the mandible. This prevents the tongue from falling backwards and obstructing respiration. Hence this muscle is known as the safety muscle of the tongue.

The given case scenario is suggestive of damage to the facial nerve above the level of the stylomastoid foramen, resulting in injury to chorda tympani nerve.

Taste sensation from the anterior 2/3rd of the tongue is carried by chorda tympani nerve, whereas general sensation is carried by the lingual nerve.

Primordial germ cells originate in the epiblast, during the 2nd week of development.

Primordial germ cells (PGCs) are also known as primitive sex cells. During the 2nd week of development, they originate in the epiblast at the caudal end of the primitive streak.

They are the precursors of gametes in both genders. They pass through the primitive streak during gastrulation and reach the wall of the yolk sac. They migrate from the yolk sac in the 4th week and reach the developing gonads by the end of the 5th week.

Leptotene and zygotene are stages of prophase 1 of meiosis I.

Meiosis is a special type of cell division that reduces the chromosome number by half. It creates 4 daughter cells, each with haploid chromosomes distinct from the parent cell. Meiosis consists of two successive divisions called the first and second meiotic divisions. The various stages of meiosis are as follows:

First meiotic division (meiosis I)

• Prophase 1 (Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis)
• Metaphase 1
• Anaphase 1
• Telophase 1

Second meiotic division (meiosis II)

• Prophase 2
• Metaphase 2
• Anaphase 2
• Telophase 2

Gastrulation occurs during the embryonic period at the 3rd week of gestation.

During the 3rd week of intra-uterine life, three definitive germ layers are

formed, namely ectoderm, mesoderm, and endoderm. The three germ layers develop from the epiblast by a process of cell proliferation and migration known as gastrulation. This transforms the bilaminar germ disc into a trilaminar structure.

Primordial germ cells (PGCs) remain dormant in the testis until puberty.

At puberty, PGCs differentiate into spermatogonial stem cells. These spermatogonial stem cells then give rise to type A spermatogonia. This marks the beginning of spermatogenesis.

Secondary spermatocytes have haploid number of chromosomes.

During the process of spermatogenesis, each primary spermatocyte gives rise to 4 sperm cells (in contrast, each primary oocyte gives rise to only 1 ovum). The haploid cells formed during this process are secondary spermatocytes, spermatids, and spermatozoa.

The flowchart below shows the steps of spermatogenesis:

Spermiogenesis or spermateleosis is the process of maturation of spermatids to spermatozoa. It is the final stage of spermatogenesis.

The major events occurring during spermiogenesis include:

• Nuclear morphogenesis and condensation
• Formation of tail
• Formation of acrosome
• Rearrangement of organelles (mitochondria, centrioles, etc.)
• Shedding off excess cytoplasm

The acrosomal cap of the sperm is derived from the Golgi apparatus. Parts of the sperm and their derivatives:

The image given below shows the acrosome reaction.

Cell organelle Nucleus

Golgi apparat us

Mitochondria Centrosome

Cytoplasm

Cell membran e

Part of the sperm Head of sperm Acrosomal cap

Spiral sheath around the mid dle piece

Proximal centriole: spherical structure in sperm neckDistal centriole: the distal end of th e middle piece (annulus)

Shed as residual bodies of Re gaud

Covering of spermatozoa

Testosterone is involved in testicular descent. They are secreted by the Leydig cells.

Leydig cells are large polyhedral cells present in the connective tissue between the seminiferous tubules. Testosterone is synthesized from cholesterol in Leydig cells. The secretion of testosterone from Leydig cells is under the control of the luteinizing hormone (LH).

Primary oocytes remain dormant in the ovary until puberty. They are arrested in prophase (dicytotene/diplotene) of meiosis I and surrounded by flat epithelial cells (primordial follicles) in the ovary before puberty.

Steps of oogenesis before puberty are shown in the image below:

If the ovum is not fertilized, the corpus luteum persists for about 14 days i.e., 2 weeks. The fate of the corpus luteum depends on the fertilization of the ovum:

• No fertilization:
• Corpus luteum of menstruation remains small and secretes progesterone.
• This progesterone prepares the uterine endometrium to enter the progestational or secretory phase.
• It persists for about 14 days.
• It reaches maximum size by about 9 days after ovulation and starts to shrink 3–4 days before the next menses.
• It undergoes fibrosis to become a white scar tissue called corpus albicans.
• Ovum fertilized:
• Corpus luteum of pregnancy is formed.
• Regression of the corpus luteum is prevented by hCG secreted by the syncytiotrophoblast of the developing embryo.
• It continues to grow and secrete progesterone that helps maintain the pregnancy.
• It persists for 3-4 months until the placenta takes over.

Fertilization of the ovum commonly occurs in the ampulla of the uterine tube.

The ovulated egg enters the infundibulum of the uterine tube and then passes into the ampulla. The sperms released into the female genital tract swim to the ampulla and fertilize the ovum there.

Timeline of fertilization:

• The ovum released after ovulation is capable of being fertilized for 12-24 hours.
• The spermatozoa after ejaculation are capable of fertilization for 24-48 hours.
• Fertilization occurs within 1–2 days after ovulation.

The sperm does not penetrate the nuclear membrane of the oocyte. The three barriers for sperm penetration in the ovum include:

• Corona radiata
• Zona pellucida
• Oocyte cell membrane

After the fusion of the sperm and oocyte cell membranes, the nucleus of the ovum is converted to the female pronucleus. The nucleus of the sperm becomes the male pronucleus.

Alkaline phosphatase is not an acrosomal enzyme. The three main acrosomal enzymes include:

• Acrosin
• Hyaluronidase
• Acid phosphatase

The sperm binds to the zona pellucida through the glycoprotein ligands ZP3 and ZP2 (zona proteins). This binding causes the release of the acrosomal enzymes that allow the sperm to penetrate the zona pellucida. This is called acrosomal reaction.

Alteration of the properties of the zona pellucida to prevent the entry of other sperms is zona reaction.

After penetrating the zona, the sperm comes in contact with the oolemma (the plasma membrane of the oocyte). This contact results in weak membrane depolarization and a calcium wave.

The calcium wave triggers the release of lysosomal enzymes from the cortical granules lining the oolemma (cortical reaction). These enzymes hydrolyze the ZP3 receptor on the zona

pellucida. Digestion of ZP3 and alteration of zona pellucida (zona reaction) prevents other sperms from binding, thus creating a block to polyspermy.

The blastocyst normally implants in the functional layer of the uterine endometrium.

In the secretory phase, three layers can be recognized in the endometrium: stratum compactum, stratum spongiosum, and stratum basale. The first two layers (stratum compactum and spongiosum) are together known as stratum functionale or the functional layer.

If implantation does not occur, the functional layer is shed off during menstruation. If implantation occurs, the functional layer is retained as the decidua.

Timeline of implantation:

• 3-4 days after fertilization: The morula (12-16 cells) enters the uterus.
• 4th day after fertilization: The advanced morula reaches the uterine lumen.
• 4-5 days after fertilization: The early blastocyst stage is seen.
• 6-7 days after fertilization: The blastocyst implants in the uterus. Implantation corresponds to 20-22 days of the menstrual cycle.

The bilaminar embryonic disc is made up of the epiblast layer (columnar cells) near the amniotic cavity and the hypoblast layer (cuboidal cells) near the blastocyst cavity.

On the 8th day of development, the embryoblast differentiates into two layers, hypoblast and epiblast, to form the bilaminar disc. Around the same time, a small amniotic cavity appears within

the epiblast. At this stage, the two layers of embryoblast are arranged as follows:

• One layer of high columnar cells known as the epiblast layer, adjacent to the amniotic cavity
• One layer of small cuboidal cells known as the hypoblast layer, adjacent to the blastocyst cavity
• The image given below shows the embryonic disc with the epiblast and hypoblast layers.

Heuser's membrane or exocoelomic membrane develops from flattened cells derived from the hypoblast.

On day 9-10 of pre-embryonic development, flattened cells from the hypoblast begin to migrate to the abembryonic pole. They form a layer of cells just beneath the cytotrophoblast. This layer is called the Heuser's membrane. Once the blastocyst cavity is fully lined with Heuser's membrane, it is called the exocoelomic cavity.

The image below shows the formation of Heusner's membrane.

The parietal or somatopleuric extraembryonic mesoderm lines the amniotic cavity.

The extraembryonic mesoderm is derived from yolk sac cells. Large cavities develop in extraembryonic mesoderm, and they join to form the extraembryonic cavity (or chorionic cavity). Formation of the extraembryonic cavity splits the extraembryonic mesoderm into two layers:

• Parietal or somatopleuric extraembryonic mesoderm lining the trophoblast and outside of the amniotic cavity
• Visceral or splanchnopleuric extraembryonic mesoderm lining the outside of yolk sac
• The image given below shows the extraembryonic mesoderm.