[Reference- 100% From NCERT XI & XII ]
➡️Inside the kidney, there are two
zones, an outer cortex and an inner
medulla. The medulla is divided into a few
conical masses (medullary pyramids)
projecting into the calyces (sing.: calyx).
➡️The cortex extends in between the
medullary pyramids as renal columns called
Columns of Bertini.
➡️Collecting Duct:
This long duct extends from the cortex of the kidney
to the inner parts of the medulla. Large amounts of water could be
reabsorbed from this region to produce a concentrated urine. This segment
allows passage of small amounts of urea into the medullary interstitium
to keep up the osmolarity. It also plays a role in the maintenance of pH
and ionic balance of blood by the selective secretion of H+ and K+ ions
➡️MECHANISM OF CONCENTRATION OF THE FILTRATE
Mammals have the ability to produce a concentrated urine. The Henle’s
loop and vasa recta play a significant role in this. The flow of filtrate in
the two limbs of Henle’s loop is in opposite directions and thus forms a
counter current. The flow of blood through the two limbs of vasa recta is
also in a counter current pattern. The proximity between the Henle’s loop
and vasa recta, as well as the counter current in them help in maintaining
an increasing osmolarity towards the inner medullary interstitium, i.e.,
from 300 mOsmolL–1 in the cortex to about 1200 mOsmolL–1 in the inner
medulla. This gradient is mainly caused by NaCl and urea.
flow/glomerular blood pressure/GFR can activate the JG cells to release
renin which converts angiotensinogen in blood to angiotensin I and
further to angiotensin II. Angiotensin II, being a powerful
vasoconstrictor, increases the glomerular blood pressure and thereby
GFR. Angiotensin II also activates the adrenal cortex to release
Aldosterone. Aldosterone causes reabsorption of Na+ and water from
the distal parts of the tubule. This also leads to an increase in blood
pressure and GFR. This complex mechanism is generally known as
the Renin-Angiotensin mechanism.
An increase in blood flow to the atria of the heart can cause the release
of Atrial Natriuretic Factor (ANF). ANF can cause vasodilation (dilation of
blood vessels) and thereby decrease the blood pressure. ANF mechanism,
therefore, acts as a check on the renin-angiotensin mechanism.
on the number of axon and dendrites, the neurons are
divided into three types, i.e., multipolar (with one axon
and two or more dendrites; found in the cerebral cortex),
bipolar (with one axon and one dendrite, found in the
retina of eye) and unipolar (cell body with one axon
two types of axons, namely, myelinated and nonmyelinated.
The myelinated nerve fibres are enveloped
with Schwann cells, which form a myelin sheath
around the axon. The gaps between two adjacent
myelin sheaths are called nodes of Ranvier.
Myelinated nerve fibres are found in spinal and cranial
nerves. Unmyelinated nerve fibre is enclosed by a
Schwann cell that does not form a myelin sheath
around the axon, and is commonly found in
autonomous and the somatic neural systems.
cells which covers the cerebral hemisphere is called cerebral cortex and is
thrown into prominent folds.
matter due to its greyish appearance. The neuron cell bodies are
concentrated here giving the colour.
areas, sensory areas and large regions that are neither clearly sensory
nor motor in function. These regions called as the association areas are
responsible for complex functions like intersensory associations, memory
and communication.
➡️These action potentials (impulses) are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analysed and theimage formed on the retina is recognised based on earlier memory and
experience.
➡️Mechanism of Hearing
How does ear convert sound waves into neural impulses, which are
sensed and processed by the brain enabling us to recognise a sound ?
The external ear receives sound waves and directs them to the ear drum.
The ear drum vibrates in response to the sound waves and these vibrations
are transmitted through the ear ossicles (malleus, incus and stapes) to
the oval window. The vibrations are passed through the oval window on
to the fluid of the cochlea, where they generate waves in the lymphs. The
waves in the lymphs induce a ripple in the basilar membrane. These
movements of the basilar membrane bend the hair cells, pressing them
against the tectorial membrane. As a result, nerve impulses are generated
in the associated afferent neurons. These impulses are transmitted by
the afferent fibres via auditory nerves to the auditory cortex of the brain,
where the impulses are analysed and the sound is recognised.
➡️Nerve impulses are generated and transmitted by the
afferent fibres to the auditory cortex of the brain.
➡️ACTH
stimulates the synthesis and secretion of steroid hormones called
glucocorticoids from the adrenal cortex.
➡️Adrenal Gland
Our body has one pair of adrenal glands, one at the anterior part of each
kidney . The gland is composed of two types of tissues.
The centrally located tissue is called the adrenal medulla, and outside
this lies the adrenal cortex
➡️Underproduction of hormones by the adrenal cortex alters
carbohydrate metabolism causing acute weakness and fatigue leading
to a disease called Addison’s disease.
➡️The adrenal cortex can be divided into three layers, called zona
reticularis (inner layer), zona fasciculata (middle layer) and zona
glomerulosa (outer layer)
➡️The adrenal cortex secretes many hormones,
commonly called as corticoids. The corticoids, which are involved in
carbohydrate metabolism are called glucocorticoids. In our body, cortisol
is the main glucocorticoid. Corticoids, which regulate the balance of water
and electrolytes in our body are called mineralocorticoids. Aldosterone is
the main mineralocorticoid in our body.
➡️Small amounts of androgenic steroids are also secreted by the adrenal
cortex which play a role in the growth of axial hair, pubic hair and facial
hair during puberty.
➡️Ovaries are the primary female sex organs that produce the female
gamete (ovum) and several steroid hormones (ovarian hormones).
The ovaries are located one on each side of the lower abdomen
. Each ovary is about 2 to 4 cm in length and is connected to
the pelvic wall and uterus by ligaments. Each ovary is covered by a thin
epithelium which encloses the ovarian stroma. The stroma is divided into
two zones – a peripheral cortex and an inner medulla.
➡️
➡️The Ground Tissue System
All tissues except epidermis and vascular bundles constitute the ground
tissue. It consists of simple tissues such as parenchyma, collenchyma
and sclerenchyma. Parenchymatous cells are usually present in cortex,
pericycle, pith and medullary rays, in the primary stems and roots. In
leaves, the ground tissue consists of thin-walled chloroplast containing
cells and is called mesophyll.
➡️Dicotyledonous Root
The internal tissue
organisation is as follows:
The outermost layer is epiblema. Many of
the cells of epiblema protrude in the form of
unicellular root hairs. The cortex consists of
several layers of thin-walled parenchyma cells
with intercellular spaces. The innermost
layer of the cortex is called endodermis.
It comprises a single layer of barrel-shaped
cells without any intercellular spaces. The
tangential as well as radial walls of the
endodermal cells have a deposition of
water-impermeable, waxy material suberin
in the form of casparian strips. Next to
endodermis lies a few layers of thick-walled
parenchyomatous cells referred to as
pericycle. Initiation of lateral roots and
vascular cambium during the secondary
growth takes place in these cells. The pith
is small or inconspicuous. The
parenchymatous cells which lie between
the xylem and the phloem are called
conjuctive tissue. There are usually two
to four xylem and phloem patches. Later,
a cambium ring develops between the
xylem and phloem. All tissues on the
innerside of the endodermis such as
pericycle, vascular bundles and pith
constitute the stele.
➡️Monocotyledonous Root
The anatomy of the monocot root is similar
to the dicot root in many respects (Figure
6.6 b). It has epidermis, cortex, endodermis,
pericycle, vascular bundles and pith. As
compared to the dicot root which have fewer
xylem bundles, there are usually more than
six (polyarch) xylem bundles in the monocot
root. Pith is large and well developed.
Monocotyledonous roots do not undergo
any secondary growth.
➡️
➡️Dicotyledonous Stem
The transverse section of a typical young
dicotyledonous stem shows that the epidermis
is the outermost protective layer of the stem.
Covered with a thin layer of cuticle, it may bear trichomes and
a few stomata. The cells arranged in multiple layers between epidermis and
pericycle constitute the cortex. It consists of three sub-zones. The outer
hypodermis, consists of a few layers of collenchymatous cells just below the
epidermis, which provide mechanical strength to the young stem. Cortical
layers below hypodermis consist of rounded thin walled parenchymatous
cells with conspicuous intercellular spaces. The innermost layer of the cortex
is called the endodermis. The cells of the endodermis are rich in starch
grains and the layer is also referred to as the starch sheath
➡️The cells arranged in multiple layers between epidermis and
pericycle constitute the cortex.
➡️The innermost layer of the cortex
is called the endodermis.
➡️Cork Cambium
As the stem continues to increase in girth due to the activity of vascular
cambium, the outer cortical and epidermis layers get broken and need to
be replaced to provide new protective cell layers. Hence, sooner or later,
another meristematic tissue called cork cambium or phellogen develops,
usually in the cortex region.
➡️Phellogen is a couple of layers thick. It ismade of narrow, thin-walled and nearly rectangular cells. Phellogen cuts
off cells on both sides. The outer cells differentiate into cork or phellem
while the inner cells differentiate into secondary cortex or phelloderm.
➡️The cells of secondary cortex are parenchymatous.➡️The ground tissue system forms the main bulk of the
plant. It is divided into three zones – cortex, pericycle and pith.
➡️Most of the water flow in the roots occurs via the apoplast since the
cortical cells are loosely packed, and hence offer no resistance to water
movement. However, the inner boundary of the cortex, the endodermis,
is impervious to water because of a band of suberised matrix called the
casparian strip. Water molecules are unable to penetrate the layer, so
they are directed to wall regions that are not suberised, into the cells
proper through the membranes. The water then moves through the
symplast and again crosses a membrane to reach the cells of the xylem.
The movement of water through the root layers is ultimately symplastic
in the endodermis. This is the only
way water and other solutes can
enter the vascular cylinder.
➡️Nodule Formation
Nodule formation involves a sequence of multiple interactions between
Rhizobium and roots of the host plant. Principal stages in the nodule
formation are summarised as follows:
Rhizobia multiply and colonise the surroundings of roots and get attached
to epidermal and root hair cells. The root-hairs curl and the bacteria invade
the root-hair. An infection thread is produced carrying the bacteria into
the cortex of the root, where they initiate the nodule formation in the cortex
of the root. Then the bacteria are released from the thread into the cells
which leads to the differentiation of specialised nitrogen fixing cells. The
nodule thus formed, establishes a direct vascular connection with the host
for exchange of nutrients.
